To produce a full sound on the bass guitar you can strum two or more strings with your right hand. When you do this you will be actually playing a chord.
When you strum downwards (t) use the fingers of your right hand.
When strumming upwards (y) use the back of your thumb.
Downward strum (t) Use the back of your fingers.
Up stroke (y) Use the back of your thumb.
In Lick 25 the down stroke is used over all four strings.
In Lick 26 use an alternating downstroke up strum. To obtain the rest on the last beat of the bar place your right hand across all four strings to stop them sounding (see photo).
You can also use a pick for strumming.