Boyfriend wants fingering and pain

Hi everybody I am a lurker but now it’s time to ask. Recently my boyfriend asked me to finger him and play with his prostate and I want to go slow as it is something new that I do not have experience however he told me he wants me to cause him some pain ? He even mentioned he is in to stretching him. I am all in however I am in uncharted waters here so how would I give him pain for example ?