Verb conjugation of "separate" in English

Place the cursor (using the mouse) on the section which you want to delete. Hold down the 'Shift' key and press the 'PageDown' key or the bottom arrow key. The document should then be marked in blue.
You have to be careful when you go on summer vacation. There are many dangers but the most dangerous one is the sun itself, because if you're not careful it may harm you. People underestimate the rays.
In school, we now are learning the grammar part, more specifically, the participles and so on. I understand it at all, but the conjugations, boy they are tough. A lot of patience is needed.