New, need help with creating quality instrument sounds.

Welcome to the forum.
While you can 'play' the onscreen keyboard and drum kit, those are there just to sample the sounds; you can't record them.
You can write MIDI data (notes) in either the Staff view or Piano Roll view (PRV) with your mouse and set the MIDI track's output to the software synthesizer you select, or record your MIDI controller live and play it through a soft synth. 
You can record audio with your microphone or plug a guitar or other instrument directly into your sound card's Line-in.
You can drag and drop audio or MIDI clips into a track.
While most USB mics are fine for recording things like talking for a blog/webcast type thing, most are not suitable for multi-track recording, since they usually have to use the MME Driver Mode, the slowest audio driver there is. That makes it nearly impossible to listen to a recorded track while recording your singing because of the huge latency (delay) imposed by MME.
I see that the Yeti has direct, zero-latency monitoring, but I think that's just for the mic. Their web pages seem to suggest you monitor what is playing by listening to the speakers. Not an optimum solution.
Have you tried recording the mic while monitoring an existing track? How did it work?
Did you get SONAR LE with the mic?