A file with the extension ".tar" is an archive of one or more files. Uncompress it first locally on your own computer. Then select the files you wish to upload into Galaxy for use with tools and load those. If any are in a compressed state (such as ".gz"), that is OK, Galaxy will uncompress it in your history.
How to upload data: http://wiki.galaxyproject.org/Support#Loading_data
Use the "Upload" tool at the top of the tool menu, or the tool "Get Data: Upload File", for files < 2G. For larger files, first use FTP, then go back and use one of these to move the FTP loaded file into your history.
MACS has specific expected inputs. A link to MACS documentation is on the Galaxy tool form. Many usage examples are also on the public server in Published Pages and in our wiki under "Learn -> Tutorials". If you need more assistance with the Galaxy expected inputs/parameters for a particular use case, after loading and reviewing our help, please start a new post and explain what is going wrong in the description plus see similar posts for prior MACS questions in the right side bar here ---->
Hopefully this helps! Jen, Galaxy