Select the tool. you would like to use for a markup by clicking on the tool button. Click on the area you want to place the markup (two clicks from/to). To add text, click on the T button and enter the text you want to add in the Enter your text here box. Click on the area you want to place the text.
Click to add a stamp (approved, rejected etc). To add click on the stamp button, select the type of stamp by clicking on the name. Click on the area of the document you want to add the stamp.