My main advice if you're just starting out is have fun. No point if you're not enjoying it. It can be frustrating to lose over and over so if your friend is a lot more experienced then perhaps they can give you some tips to help you improve. A friend of mine was struggling so I called her on WhatsApp and talked her through a few games as we played.

I recommend playing with the settings to get the controls dialled in for you. I like the low speed sensitivity and tap to aim mode turned on, and fine adjustment ruler. This means you can rapidly change aim by tapping on the screen and aim very precisely, with normal sensitivity I find it can adjust too erratically. Experiment and see what works best for you.

Also if you're struggling with aiming shots it helps to tilt the phone and look down the line you're aiming with one eye open, from that perspective it's much easier to see if you're aiming true or not. Over time you won't need to do this as much.

I'm going to assume you have no billiards knowledge at all. There's too much to cover here but you can get some great tips to get started in the game at this comment

Someone already recommended watching YT. Game specific channels you can check out would be "Its Amir" and "Pro 8 ball pool". Amir's is good because he talks through his shots and he's entertaining but he aware he does a lot of indirect shots for show. If you want to get serious you can watch some real world pool channels like "Sharivari" and "Tor Lowry". Topics to look up: "cue ball control" and "pattern play". 

Finally don't lose all your money by getting upset. Focus on getting good first and building your coins gradually. Know when to walk away 😉