When the topic minor mode is turned on, a new T submap will be available. In addition, a few of the standard keys change their definitions slightly.
In general, the following kinds of operations are possible on topics. First of all, you want to create topics. Secondly, you want to put groups in topics and to move them around until you have an order you like. The third kind of operation is to show/hide parts of the whole shebang. You might want to hide a topic including its subtopics and groups, to get a better overview of the other groups.
Here is a list of the basic keys that you might need to set up topics the way you like.
gnus-topic-indent). If given a prefix, “un-indent” the topic instead.
The following two keys can be used to move groups and topics around. They work like the well-known cut and paste. C-k is like cut and C-y is like paste. Of course, this being Emacs, we use the terms kill and yank rather than cut and paste.
gnus-topic-kill-group). All groups in the topic will be removed along with the topic.
gnus-topic-yank-group). Note that all topics will be yanked before all groups.
So, to move a topic to the beginning of the list of topics, just hit C-k on it. This is like the “cut” part of cut and paste. Then, move the cursor to the beginning of the buffer (just below the “Gnus” topic) and hit C-y. This is like the “paste” part of cut and paste. Like I said—E-Z.
You can use C-k and C-y on groups as well as on topics. So you can move topics around as well as groups.
After setting up the topics the way you like them, you might wish to hide a topic, or to show it again. That's why we have the following key.
gnus-topic-select-group). When you perform this command on a group, you'll enter the group, as usual. When done on a topic line, the topic will be folded (if it was visible) or unfolded (if it was folded already). So it's basically a toggling command on topics. In addition, if you give a numerical prefix, group on that level (and lower) will be displayed.
Now for a list of other commands, in no particular order.
gnus-topic-move-group). This command uses the process/prefix convention (see Process/Prefix).
gnus-topic-copy-group). This command uses the process/prefix convention (see Process/Prefix).
gnus-topic-hide-topic). If given a prefix, hide the topic permanently.
gnus-topic-show-topic). If given a prefix, show the topic permanently.
gnus-topic-remove-group). This command is mainly useful if you have the same group in several topics and wish to remove it from one of the topics. You may also remove a group from all topics, but in that case, Gnus will add it to the root topic the next time you start Gnus. In fact, all new groups (which, naturally, don't belong to any topic) will show up in the root topic.
This command uses the process/prefix convention
gnus-topic-mark-topic). This command works recursively on sub-topics unless given a prefix.
gnus-topic-unmark-topic). This command works recursively on sub-topics unless given a prefix.
gnus-topic-expire-articles). (see Expiring Mail).
gnus-topic-edit-parameters). See Topic Parameters.