I've said this before, but I think it's worth repeating - If you are asked to sign a contract, PLEASE be sure you understand it and agree to the terms BEFORE signing it.
No reputable publisher will mind you asking questions about points you're not sure of.
If you sign something you don't understand then there's a danger you'll accidentally break the contract terms.
If you don't agree, then say so and don't sign. In some cases it may be possible to negotiate (I've successfully done this in the past when a publisher requested full exclusive rights, which I wasn't prepared to give up.)
Once you have signed (if you do) be sure you keep a copy for future reference.