This is very simple, but they are a few tips to ensure you get a nicely browned sandwich with melty cheese. Let's avoid burnt bread and raw unmelted cheese!
First, let your vegan butter come to room temperature. Something that helps is to cut it into 1 Tbsp portions and let them hangout on a plate. Try to avoid microwaving them as this can lead to uneven melting.
Next, butter your bread with about 1 Tbsp of Vegan Butter for each slice.
In a cold, non-stick or well seasoned pan, add a slice of bread butter side down, then 2 - 3 slices of Vegan Cheese, followed by the other slice of bread, butter side up.
Turn the heat to Medium Low (about a 3) and wait a few minutes. Check underneath and see how brown the bread is. If it's still pale, let it cook longer, until it does get brown. Then flip, and repeat.
This should give the cheese plenty of time to melt, but you can also cover to help trap in the heat. Just be careful as covering too long can steam and make the sandwich soggy.