Videos like the first one are mostly animation or motion graphics based, which is a different skill. While you could certainly learn how to do it yourself, you may be able to find "stock" graphics that have what you want.

The Slack one could be done by recording the screen (using any one of a number of screen recorders such as Camtasia, Screenflow, Quicktime, or a bunch of free/open-source ones) and then using their tools to highlight via animation and record a voiceover or using a dedicated video application like Adobe Premiere Pro or Apple Final Cut Pro X. Not difficult, but another skill to learn.

Remember, these videos (and many like them) are created by teams who have dedicated graphics and video folks (or hire freelancers) to do the work.

Those links look dodgy as hell, you got any examples that aren't?

Videos are generally made by professional video production companies. You can make your own on the cheap, but they'll generally look cheap.

A quick Google search will find you a plethora of $20 p/m automated video makers.

I use Kap