need to gain weight

hi guys, i'm 17f and for the past year or so i've felt kind of weird about my body, but more than that, i'm pretty unhealthy for my age, even if my build is seen as 'ideal'. i'm not extremely scarily skinny but still definitely skinny, and i'd like to be a good healthy weight. i'm also very flat from the front which i get made fun of alot for, and it makes me feel less womanly. i'm 5'7, above the average height for girls my age and i'm currently 50kg. i can't attach a picture due to religious beliefs but i hope you have an idea. i have a fast metabolism like my dad, and no matter how much i eat i just can't seem to gain anything. however, i do have a bit of belly fat, which is probably from fast food i eat 1-2x a week.

i have absolutely no clue about fitness and health and stuff, never been into it but i really want to get in shape by summer. any advice, dietary recommendations, workout plans, number of calories i should intake, burn etc i would really appreciate. may i also add that i don't have access to any gym, my parents have some dumbbells but that's pretty much it, all i can really do is youtube workouts and walks/runs.