Soccer fans, can you help?

I did not play soccer when I was young. In fact, the only people who did in school were girls. Have a question about offsides. I Googled it but I'm still in the dark about how it works. I have been watching world cup and enjoying it. It seems that there are many possible ways a player can be offsides. I understand ice hockey very well but my knowledge of hockey outside doesn't translate. Can anyone explain this for me please?