Hello everybody!
I need to add virtual drum parts for my recordings through Sonar LE x1. I opened drum kit track on the DAW but I cannot figure out how to write my own drum parts except for the default loops or beats. Is tis possible I can compose my own drumming ideas and attacks and rhythms on Sonar or I can just use the existing ones? If not, do you know any other software for that kind of work? Please help me on this, I would appreciate!

Sure - using PRV (piano roll view) -
Here is the documentation for X3 but I think X1 is essentially the same,
https://www.cakewalk.com/...amp;help=Views.04.html
Look at the "drum pane".

Might also want to lookup "drum maps" and/or do a search for a drum map for your drum synth/ sampler.

check this one too, easy to follow
https://www.youtube.com/watch?v=ruAnAPR6-hQ

There's also Cakewalk's own four-part Drum Production Master Class using Session Drummer 3 and Step Sequencer:
 
https://www.youtube.com/watch?v=-X-fIfLFtvM
 
It dates to 8.5 but is still applicable, especially for those who don't yet have a version that bundled Addictive Drums. It's a good introduction to step sequencing techniques in any case.
 
I actually have a project in which I followed the whole video series to recreate 'Seth's Groove', and posted a short piece based on it here:
 
     http://soundclick.com/share.cfm?id=11188398
 
 

brundlefly
There's also Cakewalk's own four-part Drum Production Master Class using Session Drummer 3 and Step Sequencer:
 
https://www.youtube.com/watch?v=-X-fIfLFtvM
 
It dates to 8.5 but is still applicable, especially for those who don't yet have a version that bundled Addictive Drums. It's a good introduction to step sequencing techniques in any case.
 
I actually have a project in which I followed the whole video series to recreate 'Seth's Groove', and posted a short piece based on it here:
 
     http://soundclick.com/share.cfm?id=11188398
 
 

one of my all time favorites (by seth)
I thought this video was such a great piece of work when it first came out.
(I still do)

I agree; Seth did a great job on these. I don't actually use Step Sequencer much; I prefer to record drum parts live from a keyboard. But the videos were so well done, I had to give a whirl.