Too many are just money making ventures and won't do anything for you. Of course I always recommend doing everything possible, and sometimes that includes contests to bring attention to your writing. There are only a handful of reputable ones that I know of though. A lot of new writers ask about the payments for scripts sold. And so on.
Writers often get an amount up front for the script and a bonus if the script goes into production.
500K against a million means 500K up front and another 500K if it gets made. Always get at least WGA minimums without a representative and much more with. A brief over view of the different stipulations, pay periods, perks or no perks, percents, etc. A studio contract covers the terms of the deal and is mostly designed to protect the studio's interests. Anything above that is what you negotiate for.