Click on the FX button on the channel you wish to use an effect.
Click the "+" and select the effect you wish to use in the drop down menu. Read more about the different effects here.
When you have selected an effect, the FX button will turn yellow, meaning it is active, and the FX controls will pop up.
To use the knob controls, point your cursor over a control, click and drag up or down to the desired value. Click on the Bypass button if you wish hear the track without the effect.
You can add multiple effects on one channel.
Click the "+" again and select an effect from the drop down and you have a multiple effect chain going.
You can change the order of the effects chain by holding the cursor down over the name of the effect and dragging it on top of the effect position you want to swap to.
Here the order of the effects chain is swapped.
It's possible to automate the effect parameters. Read more about automation here.