Android is an 'Operating System'. It is installed on smartphones and tablets by many manufacturers, eg Samsung, Asus, Lenovo, HTC, Medion, Huawei, and many many others. A problem is that each manufacturer customises the Android system to best suit their devices. This makes it difficult to create a generic tutorial. Plus, like the iOS system, the Android system gets updated regularly.
Android Basics Tutorial at GCFLearnFree is very good. Just do the tutorials in order
Complete Beginners at GadgetHacks website. They also have more advanced tutorials
How To Geek has a short beginners guide to getting started with an Android device
Its always worth browsing YouTube for videos that give clear tutorials without annoying voices and music. This will list videos relating to Samsung Tablet Basics, this one to Lenovo tablet basics YouTube is a fabulous resource but you do have to dig around in it. Its also important to note how old the video is as it may well be for a much older model than you have.
Samsung Galaxy phone Beginners Guide - relates to most Android Phones
Samsung has downloadable full manuals for its tablets and phones but they do seem tricky to find. As at Sep 2020 these are the links to web pages where you can download the full manual for the SM T510 Tab A 10.1" tablet and the SM-T290 Tab A 8" tablet If you have a different model (and there are plenty) then try googling for the model number manual, eg 'T515 manual'
Lenovo also has manuals and seem to be just as difficult to find. Go to this Lenovo site and then click on Tablets, select your model series and sub series. Best to have this written down first. This info maybe in fine print on the back of the device. Or go to Settings / System / About.