Plugin Clarification

I don't always understand what each plugin actually does and I have spent a lot of time installing and then deleting when I realize it wasn't what I thought. I wonder if you could tell me if there is a plugin that will allow me to post the same post to multiple blogs simultaneously verses having to post to each blog separately AND Secondly, is there a plugin that once I make a post, I can then share it to social media???
Thank you!