How can I combine multiple HDDs with LVM?

I have 2 spare HDDS and 1 SSD laying around. I want to combine them into one big volume and connect it to my server. HDD a is 2TB, HDD b is 1TB, SSD is 250GB. I have never done raids before but my 2TB HDD is almost full and I need more space so that's why I turn to raid.

Also would it be easy to add more hard drives in the future? Family members have 2 laptops with 500GB HDD and 750HDD they will be swapping them for SSDs in the near future and I would like to add them to my file server raid too.

How can I do this in Ubuntu?

Edit: So it seems that I can do this with LVM. I have seen a few guides explaining stuff but to me they're very confusing since I have limited knowledge on modifying disks aside from using GParted for partitioning. If someone could create a complete guide with screenshots for combining at least 2 hard drives, I would be very grateful. I'm sure many other Linux users looking to do the same would benefit also.