I would assume you wanted to ask how to find apps on your Android device? You can download them from the Google Play store that's already on your phone
If that is not what you asked then can you please elaborate and reformulate the question? I am not sure if that was what you asked.
The tittle of the your post and the actual content of it are both telling a different story.
Help me understand better what exactly was your question and i will be more than happy to help you with anything
Hi! If you're referring to finding your smartphone when it's lost, you have a few options:
Find My Device (Google) - Since you're using Android, you've probably connected it to a Google account. If so, as long as your phone is connected to the internet (via mobile data or WiFi) you will be able to locate it, lock it, make it ring and more! This is useful for figuring out where it's gone (e.g. if you lost it in a vehicle) or, in the worst-case scenario, erasing all your sensitive data. If the GPS on your phone isn't currently on or if the battery is dead, Google will still show the last known location of your phone. This can be pretty accurate, down to pinpointing the street. Hereis a guide to setting it up, as well as some alternatives
Cerebrus is more of an anti-theft app, since it packs a lot of security features (e.g. automatic back-up, taking photos). However, it can also help track your phone and might be more useful if you're worried about someone getting a hold of your data
Find My Mobile (Samsung) - If you have a Samsung, they also provide a tracking service. This gives you some extra features that Google doesn't, such as backing up to their cloud servers. This wouldn't be my first choice since I think Google's is more accurate, but in case Google's isn't working for you it's always good to have a fallback
Android Lost- I have not personally tried this, but it sounds fantastic. Having lost my phone before, I get very anxious about running out of battery before I find it. This app uses SMS messages to control your phone (e.g. set off an alarm) so it should use much less battery than other apps such as Google's. Plus, even when you're not connected to the internet, you can still locate your phone even if GPS isn't already on!
How to find lost mobile - This is a very similar app to Android Lost, but a little more geared towards anti-theft (e.g. automatic photo taking when sim card is changed). Additionally, the free version has most of the useful features, with Premium only offering automatic photographing when the phone is unlocked - so you're not missing out on much. Again, it uses SMS so there's no need to have internet access
Google Maps Timeline - This is more of a supplement to Find My Device since any location history should show up on Find My Device as well. However, combined with Google Photos, this might help you figure out precisely where your phone is. This requires GPS and internet connection
The easiest and fastest way to recover a lost phone is to make sure you have internet and GPS on at all times or, at the very least, whenever you go out. This is because Google's tracking feature does not require extra app installation. However, if your phone cannot access the internet then don't lose hope! Just make sure you have installed these apps before going out and make sure your phone is fully charged, because there's little you can do once your phone runs out of battery.