@primpoisepiety
Which muscles does it target mainly?
Pectorals, anterior deltoids (front shoulders), and triceps.
Based on Q.1 which day should I include pushups in? (Upper body or leg)
Push-ups are an upper body pushing exercise.
P.s- my upper body days are divided into two i.e triceps + chest and back + abs
That's good, with split programming it's generally better to hit every major compound exercise in the synonymy of motion (pushing, pulling, legs), plus you need to oblige 48 hours of recovery in between targeting muscle groups. You don't need to divide abs to a day though, they have high enough recovery that you can exercise them every day.
Where should I feel the "good" kind of muscle pain after pushups to know that the form was right and I hit the right places?
A) You should not be feeling pain
B) Soreness is not a reliable indicator of success. The primary metric of progress is performance benchmarks. Adhere to good form and pay attention to your sense of proprioception.
I only just started and currently do 4×5 pushups at least 3-4 days a week i.e all of the days I go to gym. Should I adjust to gain better results? How? If you have any advice, please share.
Frequency depends on your personal schedule. Every other day (3-4 days a week) is certainly optimal so long as you're obliging 48 hours of recovery between muscle groups (NOT just push-ups).
Do you have any tips regarding forms and such? I'm a beginner so any tips would be really appreciated.
Throughout the whole motion, your forearms and elbows shouldn't move. Keep your elbows tucked close to your sides, don't flare them out.
Visualize pushing the ground away from you.
Visualize contracting the grip inwardly on a vertical plane. For example, with bench press visualize retracting the bar in upon itself. Squeezing your arms together on the eccentric movement during a push-up will help activate the pectorals.
How well does pushup work for flappy underarms, fatty back and tummy?
Directly? None whatsoever, spot reduction is fiction.
Indirectly? A lot, putting on muscle is one of the best ways to improve your body composition. 1lb of fat burns ~2 calories just sitting around, 1lb of muscle burns ~5 calories just sitting around.