When you terminate an instance the volume is deleted. If you stop an instance the volume is kept. You can enable termination protection on an instance that prevents termination, but that's easy to disable if you have appropriate rights in IAM.
In the free tier you get a t2.micro that can run for a full year without being turned off, 30GB of disk (EBS storage, inc SSD), an RDS database instance, 5GB of S3 standard storage, plus a lot more. One catch is I don't think EBS snapshot storage is included, so you may have to pay for snapshots.
There's no need to turn your instance off if you're not using it. You have enough credit to run that server 24/7 for 12 months.
I think in your question you have terminology confused. The terms like terminate are very specific. If you terminated an instance the disk isn't there, however if you took a snapshot or created an AMI they'd still be there.
AWS isn't for beginners who want a bit of hosting, it's a huge sprawling enterprize grade infrastructure platform. I spent two years studying AWS and getting their certifications, but with a bit of reading you should be able to understand the basics of compute (EC2) and storage (EBS/EFS/S3).
AWS provides excellent documentation on all its services, as well as tutorials and beginners guide. Just type what you want to learn into Google and you'll find a huge number of resources from AWS and others. If there's anything you can't work out after reading you can post a comment and I'll try to help.
If you want basic, use AWS LightSail VMs.
Update
Something I just remembered. You can set up an instance so the volume isn't deleted on termination, using termination protection. Read the documentation here. If you set this flag when you created the instance your volume will persist after the instance is deleted.