Have you ever played a survival/crafting game? You need a cooking station to cook meat. It's extremely easy to make and available from the beginning of the game. It's under the hammer's "crafting" menu.

When you cook meat, you don't need to put it in 1-8. If you just press E on the cooking station it will load uncooked meat onto it for you. If you want to keep some meat raw but cook other types of meat, that's when you would put it in a slot (or store it in a chest and only keep the raw stuff).

Put your weapon in a 1-8 slot and hit the corresponding number to pull it out. If you have a hammer in slot 7 that you're holding and a bow in slot 1, all you have to do to switch is press 1. Put away whatever you're holding and store it on your back with R. Pressing R again will take it back out. This makes it easy to keep a shield AND weapon ready with one button press.

I hope that's somewhat helpful, I really can't tell what you're having trouble with other than the cooking. Switching weapons/tools is literally one button press. The 1-8 thing in terms of things like cooking or loading wood is only if you want to cook or burn something specific, otherwise just pressing E on the target will fill it with whatever you have. For example, you don't wanna burn Fine Wood, so if you have Fine Wood and regular Wood in your inventory you can put the regular wood in slot 1-8 and hit the number instead of E to avoid it auto-loading your Fine Wood (it will auto load the regular wood first and only use the fine wood if you run out, but it's easy to accidentally spam E so much that you end up burning it after).