entrar
To enter — sounds simple, but the preposition after it (en vs a) divides Spain and Latin America, and it often replaces 'go in' in ways English doesn't.
entrar (movement)
Moving into a space — and crucially, Spanish uses entrar where English might say 'go in.'
Entra en casa. / Entra a la casa.
Go inside / Come in.
'Entrar en' is standard in Spain; 'entrar a' is standard in Latin America. Both are correct — know your audience.
No me entra en la cabeza.
I can't get my head around it.
Figurative entrar — information not going in. Common idiom.
¿Te entra el pantalón?
Do the trousers fit?
Entrar for clothes fitting — the item either goes in (fits) or doesn't. Very colloquial.
entrar (expressions)
Entrar generates idioms around things clicking, fitting, and coming over someone.
Me ha entrado sueño / hambre.
I've started feeling sleepy / hungry.
Sueño or hunger entering you — the sensation coming over you. Vivid and very natural.
No me entra este tema.
I can't get into this topic / I can't grasp this.
Subject matter not entering the brain — academic or intellectual struggle.
Le entró el pánico.
He panicked. / Panic set in.
The panic entered him. This construction for emotions overtaking someone is very Spanish.
Tricky bit
Entrar is intransitive — you don't 'entrar something,' you enter a place. The door enters nothing: 'entrar por la puerta' (enter through the door), not 'entrar la puerta.' And remember: en vs a is a genuine regional split, not a mistake on either side.