You do not say which version of MEP you are using.
Position the timeline cursor to the end of the timeline either by dragging it or pressing the End key on your keyboard
Select the clip you want to insert and either -
for MEP 2013 - click the right blue icon (circled arrow) that appears when you hover the mouse over the clip in the media pool to insert at the cursor position
or for MEP MX and previous versions - double click the clip to be added from the media pool.
You can repeat these steps as many times as you need.
Select the clip on timeline, Zoom out the timeline using button at the screen right bottom side or use (Ctrl and dowm arrow on keyboard), from the media pool slect clip or picture you want and move to the timeline.
Additionally: To see more space on the timeline use the zoom functions available at the bottom right of the MEP screen. There are also keyboard shortcuts to commonly used settings, eg single frame resolution or show the entire project, and +/- keys for further adjustments.