Unlike Latex editors (texstudio, or texshop e.g.), it does not have the list of reserved words/commands in lateral menus to retrieve quickly something you don’t remember. But I guess there are not so many things to remember at the end though I find some combinations a bit tricky.
Once you have written some scores, a grep on them can quite rapidly give you the needed words you know you already used. And if you remember how it begins, frescobaldi proposes some automatic completions.
I met another problem which is that Lily forces chords to have the same duration for all notes. Maybe it is because I have not read the advanced manual yet.
From what I’ve learned until now, I tried to guess a way out like : < c2 {e4 r}> but it does not work. It is possible ? It is very common to have notes of different durations running in parallel in the same staff.
Usually, you have to use several voices in parallel in order to achieve this
\new Staff <<
\new Voice {\voiceOne a'2}
\new Voice {\voiceTwo e'4 r}
>>
Note that for parallel music, you have to use double brackets << ... >> whereas chords have simple ones < ... > (I remembered it was difficult to grasp for me at the beginning).