Tap the on-screen Arrows to move. You have a limited number of actions, indicated in the top left part of the screen. Tap the ACT button use the left-most action. If you don't have any actions available and you can't reach the portal, press the circle button to restart the level. In some levels, you can pick up extra actions by running into the icons in the level.

TIP: Sometimes you need to use an action just to get to the one behind it.