Do you have to pay for the bike and where do you normally find the bike racks. How do the bikes attatch to them?
You don't normally pay for a bike on local services but will have to pay and reserve in advance for intercity trains. It varies by company so check. Including all the really small print hidden somewhere deep in their websites. Bike/train commuters for example can use Virgin intercities without reservation or payment everyday - but not many of their staff know this.
Bike always go in the designated carridge. You know which one it is because it has a tiny symbol painted somewhere on it closer to one end than the other. The trick is spot this as the train arrives and run along the platform with your bike to get to the right door before the train pulls away.
Attach? You'll be lucky. Sometimes they hang from ceiling hooks as in the photo a few posts above. Make sure you can lift the weight of you bike above your head before boarding. Other times they just lean in a stack against the side. Having your bike at the bottom of the stack is not clever when the train pulls into your station. And occasionally a few jobsworth guards will come shouting down the carridge and insist you position a very pointless piece of chain, or move you bike if it's in the 'wrong' place for Health and Safety reasons.
It does vary enormously. Some companies and platform staff and guards are great. A few are complete self-gratification artists who don't know their own company / national / legal policies and would prefer you scum didn't travel and mess up their 1960s train.