I have a few tuning apps but they give me some strange info like G8 instead of G, is this number the octave?
Yes, it should be. If you want to be sure, you could test them with a tone generator on your computer (eg. see if the generated tone is properly identified by your tuner).
There are about two methods I have used to tune my violin without solely relying on my ears:
1) Using a Tuner that tells me whether my string is too sharp or flat and I can loosen/tighten the string accordingly.
2) Using an online tuner app that emits the exact pitch of each string (E,A,G,D) and by listening to it I can keep tuning my strings until they sync. It's kind of like tuning by ear but with assistance. It also helps build your hearing.
I'm not entirely sure what the "G8" means in your case. But I can tell you that each absolute pitch in western classical musical notation has a number assigned to it. The lowest starts at 0 of course. So we go from A0(27.5 Hz), B0,.... then A1,B1... and so on. A4 (440 Hz) is our standard concert pitch. So yes, it does indicate octaves. however, as far as I'm concerned we tune to G3 in the violin (G below middle C or C4) not G8 so I find this confusing. I don't think it's even possible to play a note that high on the violin.
The best thing you could do for yourself is to try and learn to tune by ear. It's really not that hard: Use an electronic tuner to get your A, then play A and D together. Listen to the beats, the rapid pulsations in the sound that get faster as you move away from the correct pitch, and get slower and disappear when your D hits the right pitch...
Then, play D and G together. Notice how the beats here are less sensitive to change, and usually go slower overall.
Be careful when playing A and E together, as the beats will be fast and very sensitive to the smallest changes to tuning.
Your goal is to have no beats or dissonances whatsoever. When you think you're done, check them all with an electronic tuner, and adjust accordingly. Eventually, you will be able to do it perfectly, much faster than using an electronic tuner.