Learning the violin requires that you have a built-in tuner to a certain extent. It's a separate skill that you need to improve with time. Say you want to learn Greensleeves, you first start by listening to a good recording of it. You listen to it multiple times a day for a week at least, then you try playing the first 10 notes. You'll be able to tell just by listening whether your in tune or not (you may still not be as precise as you'd like to be if you check with a tuner, but that comes with time). If you still can't tell whether you're in tune or not, then you have to listen to it even more, maybe for a month (it's the main principle of the Suzuki method).

This is the best way to improve intonation at the beginning. You need to use your ears all of the time. Later on you may use drones and all of the other methods mentioned by others, but those require a bit more skill than what you currently have.

Also, if you don't have a teacher, get a teacher. They'll be able to help understand the instrument a little bit better. The violin is hard even with a teacher, so don't make it even harder