iPad is a tablet (that runs iOS, keyboards optional). Microsoft Surface is a tablet that runs Windows 10 (comes with keyboard). There are a number of other Windows tablets (or laptops with detachable keyboards), but most of the rest of the tablets on the market today are running Android OS (from Google).
iPads come in a couple different screen sizes (Mini), different weights (Air), performance levels (Pro) and all models offer a range of storage sizes. iPads come with or without mobile data capability, all have WiFi.
Surface tablets come at different performance levels, with Surface Book and Surface Pro operating at laptop levels, with 13 inch screens and capable of handling almost any Windows application that can deal with the amount of storage available. Surface 3 is Atom processor instead of Core family, 11 inch screen, lightest package in the family. Surface is probably the most expensive of the Windows tablet-style laptops available, other brands can be $200 and under.
Android tablets start well under $100 and go to over $600, depending on screen size and quality, processors, memory, storage, connectivity, and other hardware options.
Following my oldest daughter's example, I started with an iPad2 (for my wife, when she got too weak to hold an laptop in her hospital bed) which I am still using four years later, for Internet access from my easy chair and while traveling (I got it with 3G data capability). It shares information with an iPhone I bought a couple years later, through Apple and Google cloud storages.
My granddaughters bought Kindle Fire tablets, which are full function WiFi tablets, because they were cheap, but use them only as readers and game machines, borrowing their mom's iPad for heavier Internet work (like shopping) and using iPhones for their social connectivity.
My youngest daughter has a Galaxy Tab (I think 8 inch) with data connectivity which she uses while mobile, but still uses a 15-inch laptop for most of her school work. She uses Google cloud storage to connect the two and share data (her university account also uses Google shared storage).
Issues in choosing:
How much do you want to pay?
What intellectual investment do already have in an operating system's style?
What applications do you use offline?
How much storage to you need?
How portable do you want it to be (pocket, purse, book bag, backpack)?
Do you want to read it in bed (e.g. my original size Nook is easy to hold and read, the iPad I find too big, would need the Mini for reading in bed).
Do you have other devices for which you want to share information (e.g. Apple plays with Apple, Windows plays with Windows, though Google has sharing apps for all platforms if you will synch through Google).