verifying which of my files were pushed

verifying which of my files were pushed

I'm using git. And try SourceTree (is it free?)
I have committed and pushed files from local branch a to remote origin\a.
A colleague merged from origin\a to origin\b and I have pulled a local b.
I don't see my changes in local b.
1) How can I see all the files I have pushed to origin\a in the last week?
(ui-tool? and cmd?)
2) how can I explore remote branches without pulling them? (ui-tool? and
cmd?)
3) How can from origin\b to local a, even though they are not configured
as one being trackable of the other?
4) Any recommendation for freeware