When you post in a community, on steempeak it will go into your all post section, if you want it to show on your blog go into your All Post section, find your post, click on the three dots ... and choose Add to blog from the drop down menu. Then it will show on your blog page.

Before choosing the cross post function you want to make sure the community you posted in allows cross posting and that the community you want to cross post to accepts cross posting. I think once people get used to the communities they will find them useful, especially for finding new content you like with out a lot of bull Sh*t type post, post that do not belong. After all if you want to see post about cars do you really want to see pictures of cats?