SwiftKey follows the iOS conventions for punctuation and spacing and should not feel any different from how you are used to typing.
Adding any punctuation will place the cursor at the end of the punctuation mark so that you will need to add your own space to get to the next word. The only exception to this is the 'Quick Period'. This can be enabled or disabled in the 'Settings' menu accessed from the SwiftKey Settings. When you tap space bar twice quickly it will insert a period at the end of the last word as well as a space.
You can get to your punctuation and alternate keys by tapping the '123' key (or the '.?123' key on iPad) at the bottom left of your keyboard. On the iPhone or iPod Touch you can also easily add punctuation using the SwiftKey punctuation slider. When you tap and hold the period key, you will see a drawer of punctuation marks. You can simply slide your finger around the box in vertical alignment with the punctuation mark you like.
For further help on using the punctuation slider, please watch this instructional video:
Video captions are available here.