This will explain the terminology and the basic concepts of smartapps and device type handlers. ( The thread title is a clickable link. Note that this thread is also on the get started list.)
And this one is the old “intro to scheduling” FAQ. The problem is that smartthings is In a major period of transition right now: new app, new cloud, new rules engine, new hub. But nothing is quite finished yet, so many people are having to use both the old and the new in order to get all the functionality that they want. And if you are using the new (which is required to set up the new hubs), it is missing some of the features from the old. So it’s all pretty confusing for everybody right now.
( this is a clickable link)
If you only want to stick with the new app, that’s fine, but then you should just use the official knowledgebase articles that @sidjohn1 linked to above, and a lot of the stuff in the forum will not make any sense to you.
If you want to use both apps, which is what many people are doing right now, then there will be a lot more to absorb, but you will also get a lot more functionality out of your system and be able to use many more devices. So that’s really up to you.
People in the forum will always be glad to help if you get confused at any one point.
Oh, and before I forget, here is the community FAQ on modes, and it should clear up the confusion and applies to both the new and the old app although the terminology is just a bit different:
