New to 40k. Just bought what I could. Need help.

Everything I have googled so far is confusing to me or not what im looking for. I bought Grey Knights to start. I have no knowledge of how to play the game, but want to get my figures put together so I can start to learn. I currently have a box of 10 miniature strike squad. Which i believe can be purifiers/etc. I have a box of 5 paladins which I will make terminators. A Librarian and a dreadknight. I opened the boxes today to begin assembly and quickly learned that there are a lot of weapon choices that come in them. I have no idea what weapons to put on any of them. I dont want to just do what looks cool. I want to put them together to be what is best and what will translate into a good army composition when I learn the game and begin to build an army composition that I want and understand. I understand the game is for fun, but I want to make the very best out of what I have while translating good later. Thanks all!