Intangibles are the little things a player does to separate himself, the things you can't teach.
Durability is how likely they are to make it through an entire season with a heavy workload. Having a high durability rating for a RB is great because you can use them a ton and not have to worry very much about a drop in their performance or them getting injured.
Production is how well they're actually doing. If you're having a QB battle, the one that produces better for you on the field should have a better rating here. Helps decide who to start if you're unsure of who to use.
As for size, I'm going to assume that deals with the prototypical size for that position and how it'll effect their game. I'm also assuming that physical is how much they look to make contact and how good they are at it. I'm not really sure on
size &
physical, but those are my guesses.