Lithuania is a select-able nation in Europa Universalis IV at the beginning in 1444. Its government type is a Duchy}}
Lithuania is a very fun country to play with because you have a lot of options to expand and at the same time you don't have any.
Your country is just converted to catholic but your Tolerance of Heretic is pretty high so let the Orthodox people live there until you get event popping that provinces are converting to catholic. Be aware of Austria's opinion of you if you are lucky enough you can get alliance with:
Austria, Sweden, Livonian order
You can get a pu with poland when you become a kingdom so be aware of that too
You can also support independence with Georgia at one point and diplo vassalize them so that should help you a lot to expand to south and if you got a good friends you can take on ottomans and get Bizantium back from their grave and be a very good friends with them
Here you can see how i played it all out.
And always be aware of Coalitions and Unrest!!!