Unfortunately I don't think he mentions transformer less power supplies.
There are also many other things he doesn't mention in that video.
I figured as much; can you share some?
I only mention it (as it pertains mostly with power supplies) as I recently made that mistake 
It would be dangerous for me to make a few off-the-cuff remarks where personal safety is concerned. I might express myself poorly, not mention something that is obvious to me (but not to you), etc, - and you might hurt yourself.
A good starting point is the websites of reputable oscilloscope manufacturers. They have many pdf documents about why their equipment is the way it is, and how to use it. Tektronix is particularly good , as is HP/Agilent/Keysight.
Have a look at
You definitely can use a scope to look at digital signals, but you will need to be aware of the relationship between time and frequency, and of probing techniques.
The information below is probably more advanced than you need at this stage. It is a cut-and-paste of something that I have told other people in similar circumstances.
A key point is that for digital circuits a good strategy is to:
- first use a scope to ensure the really-analogue-but-interpreted-as-digital signals are clean (i.e. good power and signal integrity), being careful of the way the scope and probe interact with the circuit
- then debug digital problems in the digital domain, using logic analysers, or single stepping through your code, or using printf logging statement
For RF circuits, you probably want to avoid using scopes:
- for RF signals: spectrum analysers have a much more appropriate noise linearity and dynamic range specifications
- for RF components: vector & network analysers have similar advantages
but scopes are more useful when looking at the demodulated signals or simple power envelope.
Remember the key equation for scopes and probes:
t
risetime = 0.35 / bandwidth (e.g. 3.5ns <=> 100MHz, and the fundamental frequency/period is irrelevant)
In an ideal world you would have the scope's risetime sufficiently short that it can capture the fifth harmonic of the signal's risetime, e.g a 500MHz scope+probe for a 3.5ns signal risetime; in practice you can usually infer what's happening using a lower bandwidth scope.
Rules of thumb for signals and suitable probes, but remember that rules can be broken:
- audio frequency analogue <-> croc(k)-clip or *1 probe
- <50MHz analogue or low-speed digital <-> *10 probe
- RF <-> 50ohm coax or very expensive active probes
- digital <-> 500ohm low-impedance Z0 probe, or very expensive active probes, (or *10 probe)
- special purpose <-> differential probes, high voltage probes, current probes
N.B. you can't make your own *1 or *10 probe, but you can easily make your own 500ohm low impedance Z0 probe; see below.
Scope safety:
And for probe fanatics:
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