Gilles already described the process nicely but note that there is little you can do to avoid falsification. The cheques themselves have a few safety features but the cheque book can be stolen and I think that it's even legal to write a cheque on regular paper if your bank contract allows it. Of course, using your cheques would require forging your signature so that's something you could protect but it can usually be found on your credit cards, ID, etc. and isn't checked very thoroughly either.
You're really protected by the fact that you can always contest a cheque and that a “chèque barré” cannot easily be cashed (the payee therefore needs to have a bank account and reveal his ID to a bank, which is not very attractive to a fraudster). In fact, it can happen that the payee “sees” the money on his account but that his bank removes it a couple of weeks later if it turns out that the cheque was fraudulent or “sans provision” (i.e. the payer had not enough funds to back it).
All this costs the banks (processing, disputes) and merchants a lot and they don't like cheques for this reason but you, the user, are mostly safe. That's also why more and more merchants don't want cheques anymore or ask for one or two means of ID and write down your ID card's code and the like. If they have the right equipment, they can also verify the cheque against a national database to make sure it wasn't stolen and you are not “interdit bancaire”.