When making something for people to use, a website for example, you have to think about how people will be using your site. Will they have to click a lot of buttons, will they have to ask a lot of questions? While working online, you use different human factors; eg, you’re watching the screen (visual), you’re typing (motor), or you’re thinking about the information that you’re receiving (cognitive). Each one of these is considered a load. All the loads are at different levels of difficulty. Make a website with the right amount of loads that you want for your target audience.
Slide 2
Cognitive
Cognitive loads are considered the hardest because you’re actually using your brain to think (and if you don’t care so much for that, then yes, it’s really hard)
The visual load is really mostly just about seeing what’s important. It’s not too hard (unless someone’s doing a word search, those suckers are annoying)
Basically its physical activity, like moving a mouse or your finger to press on something. (and It's considered one of the least expensive load, because it doesn't take a lot of brain power) So it should be the one most used.
Continuing off of motor skills, even though its considered the least expensive, you have to be aware to make things easy for them using Fitts Law.
Use this website below and scroll down a bit and play around with the test area. It's great practice for understanding it.
http://simonwallner.at/ext/fitts/