Th excellent video will give you a good guide.
In Line Nymphing
For beginners the lengths of leaders may sound too long.
Cut your cast to 2 flies and reduce the leader length to what you can handle with ease.
The length of cast must be suited to depth water your fishing in.
No sense your point fly trailing in the bottom rubbish.
This method presents the flies in their natural pose ,static or very little movement.
It can’t be stressed enough about leaving the flies static till the cruising trout find them.
This as it says a bung a float call it what you like but this method catches trout.I fish my flies under an Entwistle Popper its deadly.
2 or 3 flies under the popper fished static or on the drift whatever you can manage.
Washing Line method
I substitute an Entwistle Plopper for the booby nymph.
This is my my second most prolific method or catching trout.
Takes are explosive and at times very gentle.