At C1 you master perception verbs with -ing/bare infinitive, complex causative structures, and the subtle distinction between "have someone do" and "have something done".
have/get something done
She had her hair cut. (arranged service)
have someone do
I had the cleaner come at 9. (instruction/arrangement)
get someone to do
I got him to apologise. (persuasion)
make someone do
She made me wait. (force/cause)
Perception verbs + bare infinitive vs -ing
+ bare inf (complete action)
I saw him leave.
whole action witnessed
We heard her sing the song.
+ -ing (action in progress)
I saw him leaving.
caught a moment of it
We heard her singing while we cooked.
Perception verbs: see, hear, watch, notice, observe, feel + object + bare inf (complete) OR + object + -ing (ongoing).
Causative with "make" — passive twist
Active
She made me apologise. (bare infinitive)
Passive
I was made to apologise. (to infinitive returns!)
Active
They made him stay.
Passive
He was made to stay.
"Make" takes bare infinitive in active but "to + infinitive" in passive. This is a famous C1/C2 exam trap.
Help — flexible structure
help + bare inf
She helped me find the answer.
help + to inf
She helped me to find the answer.
help + object + with
She helped me with the project.
can't help + -ing
I can't help laughing. (cannot stop oneself)
Causative with get + ing
Start an action / process
get + ing
Let's get going. (start moving)
get someone + -ing
The teacher got the students talking. (caused/started)