Exercises for a skinny guy

So I’ve been skinny all my life, I’m 18, 5’6 at 50kg - I’m tiny I know. I want to start building up my body a bit so I’m not as self conscious - but I’m too self conscious to start the gym alone. Are there any home exercises that would be beneficial for me to do to out in some muscle mass?
I’m quite poor so I don’t have any equipment which is tricky, so weight training isn’t an too much of an option. I used to like to run but that only works out your cardio and I’ve read that it might be detrimental for skinny guys.
Advice?

Ps, I would also like some diet advice as my appetite is very poor, so I struggle to eat loads to put on weight - so any meal suggestions for breakfast and lunch?

You could try calistethics, watch some videos of what people do and then devise your own kind of workout they use mainly body weight, but if you wanted to something along the line of bicep curls you could always use items you have around the house to start with.