Hey, welcome to this fabulous world!
Let's first say that not everyone likes or expects anal. If you don't feel ready, you can always find someone who likes oral more, and start with that.
The key is communication: let them know that you're inexperienced, and see the reaction! Go with someone who makes you feel comfortable, understands your limits and listens.
But ok, talking more specifically about anal. I understand that you're mostly interested in topping. There is some preparation involved for the bottom: it's called douching, and he basically pushes some water inside his ass and lets it flow out, to clean the inside. A bottom with experience should do it, or have other techniques to make sure it's clean inside. So theoretically, no "brown" should be involved, especially when it comes to eating his ass.
But of course "accidents" can still happen, because bodies can be a bit unpredictable. It's more likely if you go quite deep inside, and if it happens, the bottom will feel embarrassed. You should reassure him and remove the condom/get cleaned.
Every ass is different, and many guys need some time to relax their hole for penetration. Rimming helps a lot, and some (gentle) fingering too, but some guys hate being fingered. If you finger, go inside very slowly, with a lot of lube, and bend your finger towards the prostate (like if you're trying to touch the base of his dick from inside).
When it comes to fucking, in the best case scenario, you put your dick on his hole, apply a
gentle pressure, and you slowly feel the hole opening up until the dick slides in. With some guys it's easier than this, and with some it takes more care. But in many cases you can't just push it in, you need to try a couple times, in which the hole will be increasingly more relaxed.
Blood shouldn't be there. If it bleeds, it's better to stop.
Oh and farts
it sometimes happens due to air remaining trapped inside, especially after sex. It's a bit like a queef, no smell involved.
Final thing: let me advise you to use a condom for anal. And a lot of lube: sex with condom and without lube is not going to work.
