The post filters menu can be found at the upper left column of the main column, just above the list of posts. This menu allows you to filter the list and see specific subsets of posts, such as posts you haven’t read yet, posts you’ve been mentioned on, etc.

s
search
c
compose new post
r
reply
e
edit
t
go to top
j
go to the next post or comment
k
go to the previous post or comment
o
toggle comment visibility
esc
cancel edit post or comment