I'm not familiar with the Samsung tablet specifically, but there should be a settings section where you can do that.

About how to change the default settings. Google the name of the oS or device + autofill settings. Sometimes it gets obnoxious and corrects a lot of stuff it should not - this usually happens when the OS gets an update. After a while it gets used to how you type and it gets better at predicting what you'll type. But it's pretty annoying !

Welcome to DU and good luck to you!

Here's how to get rid of auto-correct on the Samsung Galaxy S4.
Tap on any text field, such as a search box, e-mail body, or a browser address bar to summon the keyboard.
Tap the gear in the bottom left of the keyboard, beside the Sym button.
Tap Predictive text to turn it off and on.

I am not familiar with your device, but a quick Google search got me this:

[div class="excerpt" style="margin-right:3px; border:1px solid #bfbfbf; border-radius:0.4615em; box-shadow:-1px -1px 3px #bfbfbf inset;"]How can I personalise and turn predictive text on and off on my Samsung Galaxy device?

http://www.samsung.com/uk/support/skp/faq/870984
If that doesn't help, you might need to Google your device plus "predictive text" for more detailed instructions.

but it still happens. The really obnoxious part is Webern* you try to fix the mess autocorrect makes, it just returns the sword** to the messed up version it created in the first place.

Another big PITA is that often the tablet produces gibberish like "tghygyhis" for "this"!
________
*I typed "when" and the tablet changed it to "Webern"!

**I typed " word" but the tablet changed it to "sword."

or posted a comment that got messed up by autocorrect, and even messed up again after I have proofread to correct the autocorrect errors.

There is a button in the "settings" icon on your tablet to supposedly let you turn off the autocorrect function, but my attempt to do so on my tablets doesn't seem to actually work.

I believe most Android devices support it and it's on by default. It's handy once you get used to it, IMHO, but if you don't know it's there and 'on' you may see some odd behavior while 'typing', esp. if you don't lift your finger well off the screen between each letter.

The way it works is you create whole words simply by dragging your finger from letter to letter without removing your finger from the screen. So like plop your finger on the 'T', then w/o removing it from the screen, quickly slide it to 'H' and then over to 'E', and release finger from the screen. If you did it 'right' (it can take some practice and its not uncommon for the device to misinterpret, esp. with longer words), you should get the word 'The' + a space, ready for the next word. Hitting delete once before starting the next word should delete the whole word it just created, which is handy.

To repeat a letter twice like the word 'Thee', you just kinda swipe up/down real fast over the same letter.