Very cool you heard about Gridcoin through this post!
A few things:

1. If you want to earn by solo mining you already need a few thousand (I'd say at least 5'000 GRC) to get your reward. This is not because Gridcoin is some ponzi scheme but because Gridcoin uses Proof-of-Stake as a consensus mechanism. So you need to invest some money (maybe $30) to get started solo. If you don't want to buy you can use https://grcpool.com and start without an initial investment!

2. If you go with solo mining you need the wallet running on a pc. You're probability to create a new block and get all the reward you're owed for doing BOINC work is dependent on how many GRC you have and how long the wallet is open and running. So if you don't want to buy and keep the wallet open and running please use on of our pools: https://grcpool.com, https://grc.arikado.ru/

3. You can do BOINC work on almost any device including a simple android smartphones/tablets. If you use one of the pools you need to do some changes to the official BOINC app to make it work with the pools. The process is described here:

but I can help you or create an apk for you if you want.

If you have any questions or need some guidance you can always ask here or join our discord server: https://discord.me/page/gridcoin