The yarn used for this item (and matching shorts from another pattern) can be seen among the photos uploaded.
This is a fairly easy and quick knit (quick being less than a week which for a beginner garment is pretty quick). Based on general knitter skill level guage, I am rated to be an advanced knitter but still struggle with knit project that require immediate and above knit skill experience. Meaning experience wise for a knit garment, I still would consider myself confidence wise, a beginner but felt this patter to be pretty easy and quick to knit.
I did have to substitute the yarn for what I already own and relieved to find I had enough yarn to knit both the top and matching boy shorts (see photo/note not from the same designer).
The really cool thing about this project is, not only is there a free pattern, but there is also an instructional YouTube video too. :-)
I do not know about you but I do luv visual aids by way of video.

If you would like to knit up the shorts, head on over to the raftsy website for the free pattern for them and you too, can make a PJ or lounge set. Depending on the hoice of yarn, you could even make a nice wRm weather attire to wearoufdoorx too.
https://www.craftsy.com/knitting/patterns/fixation-boy-sh...
Happy knitting!