MadWay Listen .... HTML Head Items will help you place your this MadWay script async code, Just add or paste the code and turn it on from extension.
And davwheat ad units is for to place Ad units by manually on the pages like header, bottom, left, right, between.
Google has 2 types of ads (for now) - Auto and manual one
If anyone doesn't know how to place ads then google will do it for yourself, you have to just put that one line "<script async" code between <head> ..... </head>
And the second one is manual which almost everyone prefers because google Ad unit AI is not that good, so we use this extension to place ads and control their position.
Now if you want to know how to place just go on youtube and you will find tons of tutorials about it.