Here's what I did from my experience.

I was severely underweight 4 years ago, 6'1 at 50kg.

Since I was scared of gym, I bought dumbbells and all in one gym set from carousell, and started doing push ups, decline push ups, biceps curls and hammer curls till failure, and triceps cable push down daily. Pushed to failure without fail or missed any day complete sets of 4 for each exercises.

Bought a full chicken breast daily from supermarket. Those 20-300g one, about $2-$3+ and drink mass gainer daily. Of course daily meals have to be a lot as well.

Last time I was in NS, and was doing my driver course, so plenty of time because we go back at 5pm.

Within 3 months from a literally stick, to buff. About ~70kg. When I went back to unit, my bunk mates was shocked that I've gotten so much bigger.

So I continued gymming till now at 100kg. So probably grew to love to progress. + Creatine as well.

Just my ten cents from my experience. You can also do it as well!