Taut-line hitch
Sliding knot for fastening loads or setting guy-lines https://www.netknots.com/rope_knots/tautline-hitch
Bowline
Essential general knot for tying a loop. https://www.netknots.com/rope_knots/bowline
Square Knot
Used for joining ropes or just an easy to unite knot. For joining ropes you could do a sheet bend which is stronger https://www.netknots.com/rope_knots/square-knot
https://www.netknots.com/rope_knots/sheet-bend
There are a billion options so I recommend just picking a few and practicing until you can tie them quickly without references. You'll start to understand hope knots in general work and be able to pick up other knots much easier.
If you care about safety, look for knots used in climbing instead.
Taut-line hitch
Sliding knot for fastening loads or setting guy-lines https://www.netknots.com/rope_knots/tautline-hitch
Bowline
Essential general knot for tying a loop. https://www.netknots.com/rope_knots/bowline
Square Knot
Used for joining ropes or just an easy to unite knot. For joining ropes you could do a sheet bend which is stronger https://www.netknots.com/rope_knots/square-knot
https://www.netknots.com/rope_knots/sheet-bend
There are a billion options so I recommend just picking a few and practicing until you can tie them quickly without references. You'll start to understand hope knots in general work and be able to pick up other knots much easier.