To search for something press s or / and the focus will be placed in the search box. Hit the Enter key when you have entered your search word(s). If you want to search for something again, just press the s or / key again and enter another search word.
If you know the issue number (aka. issue ID) of an issue you want to go to, press the # key (some keyboards might require a Shift press first) and a dialog box will open to ask you for the issue number. You don't have to enter all the padded zeros or the # symbol itself but it should work nomatter what you enter as long as it is a possible issue reference.
On any page where there is a list of links to issue (where the link text is the title of the issue) you can jump to the next and previous such link with the keys n and p respectively. This merely puts the focus on the next and previous links but to go to the issue page it links to you simply hit Return since the focus is on the link.