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it should be a single left click-hold-drag.

It sounds like you are experiencing a few performance bottlenecks. 1st is the computer age, it likely has low end graphics from 10 years ago right? Also internet latency.

if you open a document then press "command+D" (i think that's mac speak for CTRL+D) Then you will see your stats.

What we are looking for here is the ping time. Anything over 100ms is going to start feeling slow and laggy on a slower computer. 

If you cannot get the simple universal joint part to drag around, then you may want to give up, or buy a newer system, or it could be the internet in your area.
Your computer may just be at the threshold of minimum spec.  ¯\_(ツ)_/¯

Try Fusion360 or sketchup, being on the desktop that should eliminate the latency issue of your internet. But those are fairly easy to learn like Onshape, but you will lose a lot of features that are inherent in a cloud app like Onshape.

If you are doing this just for entertainment, maybe the collaboration tools, featurescript etc. don't matter for you anyway.

 

They are showing you that you can change the center of influence based on the position of the manipulator's origin.

Basically you drag the center circle of the manipulator, then it snaps to a point on a face, then you can move the part relative to that point.

So it looks like your limitaion when picking a graphics card will be a "pci-express 2.0 x16" that runs less than 2400mhz

This would be an ok budget card.
https://www.amazon.com/MSI-GT-710-1GD3H-LPV1/dp/B01DOFD0G8/ref=sr_1_8?dchild=1&keywords=nvidia%2Bgeforce%2Bgtx%2B970&qid=1594847999&sr=8-8&th=1

No guarantee on Onshape's performance.

how big are the models you are trying to open anyway ?

This is something we will add but was not in the first build of the feature.  Currently you will need to use a variable to define the dimension you want to reference.  More iterations to come.