How do you change a video format so that i can edit my videos with window movie maker?

Im trying to put a video onto window movie maker so that i can edit it but when I got to open it, there arent any of my videos are in my folder.How do you change a video format so that i can edit my videos with window movie maker?convert it to do so either google video converter or try one of these isquint and basically i dont know which files go into windwos maker but i suggest either mp4 or avi and im sure theres a file converter that will do so cause there popular formats