Since most topics in the manual should be indexed, you should try the index search first before the text search. The i command prompts you for a subject and then looks up that subject in the indices. If it finds an index entry with the subject you typed, it goes to the node to which that index entry points. You should browse through that node to see whether the issue you are looking for is described there. If it isn't, type , one or more times to go through additional index entries which match your subject.
The i command and subsequent , commands find all index entries which include the string you typed as a substring. For each match, Info shows in the echo area the full index entry it found. Often, the text of the full index entry already gives you enough information to decide whether it is relevant to what you are looking for, so we recommend that you read what Info shows in the echo area before looking at the node it displays.
Since i looks for a substring, you can search for subjects even if you are not sure how they are spelled in the index. For example, suppose you want to find something that is pertinent to commands which complete partial input (e.g., when you type <TAB>). If you want to catch index entries that refer to “complete,” “completion,” and “completing,” you could type icomplet<RET>.
Info documents which describe programs should index the commands, options, and key sequences that the program provides. If you are looking for a description of a command, an option, or a key, just type their names when i prompts you for a topic. For example, if you want to read the description of what the C-l key does, type iC-l<RET> literally.
Emacs provides the command
Info-virtual-index, bound to the
I key. This behaves like i, but constructs a virtual
info node displaying the results of an index search, making it easier
to select the one you want.
If you aren't sure which manual documents the topic you are looking for, try the M-x info-apropos command in Emacs, or the M-x index-apropos command in the stand-alone reader. It prompts for a string and then looks up that string in all the indices of all the Info documents installed on your system.