I am not a trainer, but there are some very cool vegan YouTube channels that might help you get to where you wish to be. As to where to start to be vegan...well that depends on how healthy a vegan you want to be. You could eat Oreo cookies and French Fries every day and still call yourself vegan. I'm assuming since you want to train, bulk up, and get fit, that a healthy vegan diet is what you desire. So on that assumption, I will post some YT channels and some videos below.
There's lots of how-to videos on YT about this. I'd suggest starting with some vegan bodybuilding channels though. I just found these quickly. You can find more, if you like.
I'll just add that a whole food plant based vegan diet doesn't conflict with any fitness goals whatsoever. It is much more nutrient-dense than a diet heavy on meat and cheese. As long as you are getting enough calories it will help not hinder.
By stepping up your nutrition you will be on better footing for any physical challenge. I've become a MUCH stronger cyclist since going vegan, both in terms of power and endurance. My recovery time from tough rides is way faster too. Last fall I did a week long bikepacking trip...mountain biking while carrying all my food and camping equipment...and the day after finishing did a 50+ mile mountain bike race and absolutely crushed my expected finish time.
"Where do you get your protein?" is the most over-asked question for vegans. So I will ask in advance that you cut us some slack if we dismiss your question rudely.
After all, you deserve a break. It's the first time YOU asked it.
And even if its over-asked, it's still a valid question. Many transitioning vegans DO have trouble meeting protein requirements.
Anyway, YES, you can build muscles on a vegan diet. There are lots of examples of vegan athletes. You can google it. But here is a great list http://www.greatveganathletes.com
One of the keys to getting enough protein to build muscles is just eating enough foods. Most of these athletes eat 3000 calories or more per day. Well, they don't have to worry about gaining weight. They are working out every day.
For those of us who are NOT working out 2 + hours a day, we have to make our calories count. And mostly that means eliminating or reducing what we call "empty calories". That is calories that have little or no protein or any other nutrients.
On the top of the Hit List For Empty Calories is oil
Just 1 tbsp of oil contains 100 calories - and nothing else.
Next is sugar.
One tbsp of sugar contains 47 calories. - and nothing else.
then there are highly refined and processed grains.
Like white bread. Actually, white bread isn't THAT bad - except that it's not whole wheat bread. which is so much better.
I've already given you some suggestions on where to go to learn more about transitioning to veganism. And I would just like to add that It Is Not As Hard As It Looks. It certainly isn't rocket science. But there are more ways to do it wrong than you can count. So taking some time every day for a month to learn how is a very good investment. You can try that online course I suggested above. Or just take a book out of the library. Or check out the "Food For Thought" podcast. You can get a good Vegucation while listening to really good vegan lessons while you ARE AT the gym.