Sorry - I assumed... and you know what that means.

One of the first things I do when getting started with a new copy of Blender is change which mouse-button selects. Blender's is set by default to select with the right-mouse button - you can change that in User Preferences. To get to user preferences, you kind-of move your mouse *under the menubar at the top of the Blender screen and drag it down. The Mouse options are in the Views and Controls section.

Something that you will either hate with a passion or love like the next breath you take is the fact that blender is very much a hotkey-fired application. I happen to love that. Whilst most of the hotkey options have a menu option as well, you will find yourself flying once you get the hotkeys memorised.

So, select your mesh (currently in Object Mode and press [TAB]... now you are in Edit mode. [TAB] is a toggle. So is [A]...you select all vertices/lines/faces or none with [A].

If you want to select a group of verts/lines/faces  your mesh, there are a number of ways. [B] lets you box-select. [B] [B] makes the selection tool into a circle. You can click three verts in a row (on a line with each other, connected with the same edge) and [CTRL] [E] and select Edge-Loop Select.

I could go on... but yeah, the fine manual covers a lot of this stuff better than I do.

Here's an awesome Site:
blenderunderground.com/resources/

and there's a thread on the Blender forum on here that is dedicated to Blender resources... they are legion.

To para-quote Cheech from Up In Smoke: "Hope you're not busy for a couple of years..."

Monterey/Mint21.x/Win10 - Blender3.x - PP11.3(cm) - Musescore3.6.2

Wir sind gewohnt, daß die Menschen verhöhnen was sie nicht verstehen
[it is clear that humans have contempt for that which they do not understand] 

Metaphor of Chooks