This is also known as a blow job. A penis does not need to be erect for you to start oral sex but you can use your hand to arouse him first. If you hold the penis during oral sex, you can control how deep it goes into your mouth. You can move your hand allowing the penis to go as far into your mouth as you are comfortable with.
A penis is highly sensitive, so be gentle at first and slowly work up to a faster pace. You can try moving your tongue, mouth and head in different ways to see what works best for them, but never use your teeth unless asked.
When you give a man (or anyone with a penis) oral sex you can stop at any time and it’s up to you to decide if you want to let him ejaculate (or cum) in your mouth. If he’s wearing a condom this isn’t an issue, and it means you will both be protected against STIs.
