My friends and I want to start a campaign. We don't know the ruling for the game. We are waiting for our official book to come in so we can start our first session. Can anyone explain in a simplistic manner the rules for D&D? Classes and Races we will review ourselves. Just want to know the basics.
Besides reading the Basic Rules, which someone else has already linked, I suggest you check out a game on Youtube. Note that usually these aren't an accurate representation of how most games actually go- Critical Role for instance is comprised entirely of experienced voice actors- but it'll give you an impression of how the game runs.
Just don't base your expectations of your players/dm on them.
The simplest explanation: roll to hit, then roll for damage. Or roll a save if it doesn't need to hit. Or roll a skill check if you're trying to attempt something out of combat.
That's about it. You can find the details in the rulebooks.