How do I go "Back" on the touchscreen

You can also navigate back and forward in IE by using two fingers - swipe with them horizontaly anywhere on the page.

Nope, you just need ONE finger.

It depends on where you want to go back to.

If you want to revisit a just-seen page in Internet Explorer, for example, try sliding your finger across the middle of the page to the right. That brings the previous page back into view. (You can also slide your finger inward a bit from the screen's top to fetch the menu; then tap the left-pointing arrow in the screen's bottom-left corner.)

Or, if you want to return to the app you were just using, slide your finger from the screen's left edge inward. Your previously used app will slide into view onscreen.

There is usually a back button it the upper left corner of the screen for this purpose. Some applications also offer navigation via the top toolbar: swipe down from the top edge or swipe up from the bottom edge or click with the right mouse button somewhere in an app to show it.

Internet Explorer also have a back button, but it is only available on the bottom toolbar, next to the address bar. You can also navigate back and forward in IE by using two fingers - swipe with them horizontaly anywhere on the page. When using mouse, go near the left side to uncover another back button alternative.

If there is no button in an app and you still want to go back somehow, you probably want to go to the Start Screen. In that case, just use the Start button on your device, keyboard, in the bottom left corner (go there with your mouse), or in the middle of the charms bar (swipe from the right edge to show it).

If I have not covered your case, I would say that the app you are trying to use is probably very poorly designed. Get rid off it and use another one.