gugu gaga, gaga gu--
just kidding, my bad.

TLDR:
If you understand Hashmap in Java, or Dictionary in Python, or Javascript Object. Yes, Redis work like that way. Storing your data in Memory / RAM.

Longer explanation:
Redis is actually a database, but different storing mechanism.
Traditional Relational database like MySQL or PostgreSQL will store their data to disks (HDD or SSD).
But Redis, by default storing the data to your RAM/Memory, making it faster to access or to write compared to MySQL or other Relational database. It usually used for caching. So you can access frequently-used data faster compared to accessing it to MySQL (or any other database).
But at some point, you can also store the data in Redis into your disks (for backup purposes), usually this called Redis Persistence or Redis Snapshot.

If you want some videos i recommend:
youtube.com/watch?v=5TRFpFBccQM
youtu.be/G1rOthIU-uo

Redis is just like any other database, but with some features that are specific for a certain use case.

Redis is primarily known for caching, because it is blazing fast. But in the recent years, Redis has evolved to become a fully-fledged database for apps. It supports Key-Value database (like etcd/memcached), Graph database (like Neo4j), fast search (RedisSearch), supports JSON (like MongoDB), and many more features.

So, if you're into using Redis in your app but not sure how to use it, you can search for Redis Hackathon on the search bar, you can see a lot of apps built using only Redis that is a great start to look for an inspiration.

But of course, the database paradigm is a bit different, Redis doesn't use SQL or JS-like query like in Mongo. But I think it is worth trying to use Redis as your main database.