There are an array of different types of dyes, coatings, conditioners, and techniques used to finish veg tanned leather. (Too many to list here.). To try and explain what's needed here would do you an injustice. YouTube is your friend. A lot of what I've learned about leathercraft came from the internet. Tandy Leather has a ton of instructional videos on YouTube on just about anything related to leatherworking. You'll find all you need for the basics of finishing leather there. It's a great resource.
Beleive it or not, you have one of the best resources right in front of you.....Leatherworker.net. If you go to the section “How It’s Done”, you’ll find a wealth of information and will answer many of your questions.