You might attend a meeting. Someone might ask or require you to attend a meeting, or you could attend one because you want to be there.
If you participate in a meeting, you might be in charge of the meeting, be a speaker at the meeting, or volunteer to do something at the meeting. You would not just be attending, or listening to others, but in this case you would have something to do with the leadership of the meeting. You would be more involved if you are participating.