Meditation is mostly boring. The marketing makes it sound like enlightenment is around the corner; in practice it is twenty minutes of watching your breath while your mind wanders to laundry. The benefits arrive slowly and indirectly.
Where to start
Start with five minutes a day, not twenty. Five minutes is short enough that you cannot reasonably skip it; twenty leads to skipped days and abandonment within a month.
What matters most
Posture matters less than you think. Sit on a chair with feet flat. The cushion-and-cross-legged ideal is not the goal — the goal is to be comfortable enough to be still without falling asleep.
What to skip
Apps are useful at first and become a crutch later. After the first few months, sit without one. Listening to a guided voice forever bypasses the actual practice.