The right tools for the job are key and can make the difference.
Crimp Tool
The most important too to get right is the crimp tool - use a ratcheting crimp tool, like this one
crimp tool
These ratcheting tools come with different jaws for various crimps, pick one with the Red/Blue/Yellow markings on the jaw to ensure they will work with the crimps detailed below.
Do not be tempted to use the pressed steel type, non ratcheting crimp tool, like this one with the wire stripper built in. They do not produce very good crimp connections that will fail quickly.

Wire Strippers
Wire strippers come in many different forms, use the right size for the gauge of cable being stripped. Too small and the conductor can be damaged, too large and much more effort will be required to strip the insulation off.
I use this type of wire stripper with great success
Crimps
The different colour crimps accept different diameters or wire of combination of wires.
Manufacturers vary slightly, but this is a good guide.
Red Connectors: 0.4mm to 1mm² / 22-16 awg cable
Blue Connectors: 1.1mm to 2.6mm² / 16-14 awg cable
Yellow Connectors: 2.5mm to 6.5mm² / 12-10 awg cable
Each of the connector types comes in each colour, so there are plenty of combinations to cover most eventualities if you have a good assortment of crimps available
The Crimping Procedure
Used in the video is Wire Stripper and Ratchet Crimp Tool. Strip the insulation from the multi stranded wire, twist the strands together, insert the wire into the correct sized crimp, insert the wire and crimp into the crimp tool noting the wire is showing on the side with the red/blue/yellow painted dots. Squeeze the handles until the tool releases.
If you need to extend some cabling or make repairs you may need some extra cable - various colours and suitable sizes available here on ebay with good choice of colours.