There are quite a few really useful keyboard shortcuts available on lesson pages, and some of them are not even completely explained under the "?" symbol in the bottom right corner, so I thought it would be useful to post a little reference guide here:
Navigation:
Left and Right arrow keys – move to the previous/next highlighted word
Shift+Left and Shift+Right – go to the previous/next page
b – jump to the next blue word
+ (plus) and - (minus) – increase or decrease font size
Space – stop/play audio
On any word (blue or yellow), you can do the following:
k – mark the word as known
x – "ignore"
f – open the preferred dictionary
s – play the automatically generated text-to-speech audio
On a blue word:
Up and Down arrow keys – move up or down in the list of hints and dictionaries
Enter – create a lingq with the selected hint or open the selected dictionary
e – like enter, but additionally opens a popup with the preferred dictionary
h – creates a new (empty) lingq and focuses the "hint" text field
(Shift+f – flags selected hint as wrong)
On a yellow word (lingq):
1, 2, 3, 4 – change the status of the word
h – focus the text field with the hint
t – add a tag
Hope this helps :).