Two question! First one is Simple. To understand how a coin works, you need to Google search and know youself from article related to that coin or go to that coin's telegram account and ask there what you want to know. Admin and others member will guide you and give you info. Coin price is low during token sale. If they late, fail to give you satisfactory answer or you find something phishy then avoid the project. But it hard to know which project will success.
It's not really that hard to know if a project has got potential or is worthy for an investment. However, going into their official channels and asking their team regarding the project wouldn't give you a clear idea, nor you should trust any article published regarding a project because this is usually a part of their marketing where they ask some writer to write and publish articles regarding their project so that people read that and think that the project is good.
What you need to do is follow the project through all their channels, follow their progress to see what they are doing and whether they are following their roadmap and stuff, you need to check if they have a good team, you need to read their whitepaper and then see if they are doing what they've described there, you should also check their activity and user engagements on their social channels. There are lot of other things but these should be enough to give you a general idea about a project.