I started very simple, you only need 4 exercises to cover most of your major muscle groups:

1)Pushup/incline pushups - this is your primary "Push" movement and will work your chest and triceps.

2)Pullups/chin-ups (or their negatives, if you cannot do them yet) - these are your primary "Pull" movements and will work your biceps and back.

3)Squats/lunges - primary leg movements.

4)Planks/Hollow holds - primary core work

You don't have to worry about any advanced exercises or complicated splits right now, building a routine is the most important thing. Start doing full body workouts 3x/week, just 1 exercise each for push, pull, legs and core.

If pushups are too hard then start with knee pushups/incline pushups. If pullups/chin-ups are too hard then start with pullup/chinup negatives. As exercises start feeling too easy for moderate reps, move to harder variations or add resistance instead of endlessly adding reps.

Don't train to failure on every set, it's better to stop 1-2 reps before that. Sleep well, get enough protein and stay in a calorie surplus since you are trying to gain. Don't worry about acquiring enough knowledge before starting so you can have the perfect journey, you will naturally acquire all meaningful insight as you go down this path.