Gaining weight

Welcome!
Check out these helpful links (found in the top part of this forum)

https://community.myfitnesspal.com/en/discussion/10300326/most-helpful-posts-goal-gaining-weight-must-reads#latest

Basically you want to eat above maintenance (0.5lb per week gain or less per week) , get adequate protein (0.8-1g per lb bodyweight) and make sure you are following proper training (a progressive lifting program suited to your goals)

What are your goals and what kind of equipment do you have access to? I know many people are facing limitations so you might have to do bodyweight or lighter weight for now (which can still be quite effective and challenging if done correctly)

This link is helpful

https://community.myfitnesspal.com/en/discussion/10332083/which-lifting-program-is-the-best-for-you/p1