Very simple. That's what that 'Link' button is for ? that looks like a blue globe with a chain-link in front of it, in the second row of the Edit button toolbar, just above the post compose window, and between the 'Increase Indent' and (greyed=out) 'Unlink' buttons.
One easy way, is by going to the browser tab that contains the page you'd like to link ? and left-clicking on the pages' URL address, to highlight it, or highlighting the URL address up in the pages' address field bar by left-clicking & rolling your cursor over the full address ? and then copying the URL address ? then returning to the Android Central tab or page that you're composing your post on ? and highlighting the words you would like to have appear with the light blue (linked) color, in your post, such as your
"here" or "XYZ app" ? and then clicking on the 'Link' button, (again, in the second row of the Edit button toolbar, and also just below the 'Smiley' button) ? and then pasting the copied URL address into the [ greyed-out http:// ] field ? and then clicking 'OK'.
It's actually much much easier . . than I just made it sound. lol