A portablebelt is something so portable you can put it on your belt. It is portable. Note, this is also a very common term for a cell phone or mobile phone. You'll learn more about that in the coming levels.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
To turn on your cell phone you need to press the power button for five seconds.