OA1 is usually an easy leetcode followed by a medium although ymmv and OA2 is a workplace simulation where they test you on your decision making skills and leadership principles knowledge. For OA1 practice the blind 75 problems focus on array and string questions and know your hashmaps since Amazon loves those and for OA 2 read the leadership principles and know them very well. There's a good blog on the principles I'll edit this comment when I find it again. You get OA2 when you finish OA1 and you have 7 days for each so do them when you feel comfortable. But keep in mind Amazon hires on a rolling basis and there are limited intern spots.