Hello, when rolling for an ability check only, if I’m proficient in do I roll and the app adds my +7 PLUS my bonus proficient or does the app add everything all together? 

for instance, my Proficiency is a +6 I’m proficient in arcana +8 would it be roll (#) +8+6? 

thanks 

It rolls everything you need to roll.

If your Intelligence was +2 and Proficiency was +6 and you were proficient in Arcana then for Arcana, which uses Intelligence, your character sheet will show the +8 on it and will roll that when you click it.