Hello All in advance I am ever so sorry for how long this is.. it's a cracking little novel if you've got the time.. 
My first post here so I apologise if I make any errors/haven't adhered to some forum etiquette (I know how some forums can be!)
A little about myself I am a 21 year old project engineer for jaguar land rover, always liked bikes (usually with engines) but fancied a hybrid after several years of bmxing.. my testicles have somewhat shrank and I prefer to take things a little more on the ground now! I'm pretty mechanically minded and love to learn new skills to help others and myself.. Can't always rely on a bike shop to be open if you are stranded!
So anyway, Over the weekend I've purchased what seemed to be a nice little buy http://www.ebay.co.uk/itm/CARRERA-GRYPHON-ROAD-BIKE-20-LARGE-V-SPEC-RACER-HYBRID-CITY-FIT-CYCLYING-/221172709394?_trksid=p2047675.l2557&ssPageName=STRK:MEWAX
T&nma=true&si=GuopRIsqA6BEHeGyXiKRIwFOLQg=&orig_cvip=true&rt=nc
I've put about 30 miles on it over the weekend just nipping about. So far so good; very quick, light and is very nimble.. however all of my woes are in relation to gears, which I know absolutely NADA about coming from single speeds!
The rear derailleur is a SRAM X4 which I cannot for the life of me find a youtube video, they all seem to look a lot less complicated than mine.. and the front derailleur is a Shimano Nexava.. As far as I've already read SRAM and shimano aren't compatible so I'm really not sure, Also I'm fed up of watching youtube videos as I'm getting confused at what they mean by 'highest gear' high ring low ring etc etc is it highest by ratio or by literal height on the chainring.. maybe I'm being dense!
On the inner front chain-ring (1 of 2) if I go past about gear 5 (of 8) it's rubbing on the derailleur. I have set the lower limit of the chainring so the outer face of the chain is approx 2mm from right hand side of the derailleur edge and set the height so the front of the derailleur is sitting around 3/4mm away from the outer most larger chain ring.
The front derailleur doesn't seem to be moving as I'm switching between the rear cogs. As I'm writing this I'm thinking that I should have set the chain's low limit to the inner most side of the derailleur (frameside)? So as the chain moves to the right it is touching the 2mm that I earlier set on the lower limit.
As for the rear gearset it isn't switching into gear 8 on the because the derailleur isn't moving to the right enough so is causing the chain to 'run off'.. Looking at the back everything lines up nice and true and clean so I'm not too concerned and think if I can sort the front I'll have it all cracked.
So really I want to know if the lower limit should be set with the chain nearest the left or right (looking from above) of the front derailleur which would make sense as to why mine doesn't work.
Also is there any way of going back to a base setting? I.e. so many turns in, the screws look like they have been tampered with in the past and think this may have been the case. If I revert back to 0 and work from there.. I've had a play today too which hasn't really helped!
Apologies for how long this thread actually is!
Lew

My first post here so I apologise if I make any errors/haven't adhered to some forum etiquette (I know how some forums can be!)
A little about myself I am a 21 year old project engineer for jaguar land rover, always liked bikes (usually with engines) but fancied a hybrid after several years of bmxing.. my testicles have somewhat shrank and I prefer to take things a little more on the ground now! I'm pretty mechanically minded and love to learn new skills to help others and myself.. Can't always rely on a bike shop to be open if you are stranded!
So anyway, Over the weekend I've purchased what seemed to be a nice little buy http://www.ebay.co.uk/itm/CARRERA-GRYPHON-ROAD-BIKE-20-LARGE-V-SPEC-RACER-HYBRID-CITY-FIT-CYCLYING-/221172709394?_trksid=p2047675.l2557&ssPageName=STRK:MEWAX

I've put about 30 miles on it over the weekend just nipping about. So far so good; very quick, light and is very nimble.. however all of my woes are in relation to gears, which I know absolutely NADA about coming from single speeds!
The rear derailleur is a SRAM X4 which I cannot for the life of me find a youtube video, they all seem to look a lot less complicated than mine.. and the front derailleur is a Shimano Nexava.. As far as I've already read SRAM and shimano aren't compatible so I'm really not sure, Also I'm fed up of watching youtube videos as I'm getting confused at what they mean by 'highest gear' high ring low ring etc etc is it highest by ratio or by literal height on the chainring.. maybe I'm being dense!
On the inner front chain-ring (1 of 2) if I go past about gear 5 (of 8) it's rubbing on the derailleur. I have set the lower limit of the chainring so the outer face of the chain is approx 2mm from right hand side of the derailleur edge and set the height so the front of the derailleur is sitting around 3/4mm away from the outer most larger chain ring.
The front derailleur doesn't seem to be moving as I'm switching between the rear cogs. As I'm writing this I'm thinking that I should have set the chain's low limit to the inner most side of the derailleur (frameside)? So as the chain moves to the right it is touching the 2mm that I earlier set on the lower limit.
As for the rear gearset it isn't switching into gear 8 on the because the derailleur isn't moving to the right enough so is causing the chain to 'run off'.. Looking at the back everything lines up nice and true and clean so I'm not too concerned and think if I can sort the front I'll have it all cracked.
So really I want to know if the lower limit should be set with the chain nearest the left or right (looking from above) of the front derailleur which would make sense as to why mine doesn't work.
Also is there any way of going back to a base setting? I.e. so many turns in, the screws look like they have been tampered with in the past and think this may have been the case. If I revert back to 0 and work from there.. I've had a play today too which hasn't really helped!
Apologies for how long this thread actually is!
Lew