Should I look for another job when I be just started one?

If you get called often, it might be worth it.

Huh?  Do you need a regular, full-time job?  If so, then being on a temporary, stand-by cleaning crew isn't fulfilling that requirement, is it?  Only you know what your financial needs are.  If you like your current gig, talk with the manager or owner to find out if there is a possibility of getting hired permanently and getting more hours.  If there isn't, then you need to do what you need to do to survive. 

Yes. Continue to look for a better job, one that is more stable and can offer you the hours necessary to make a living. Your present job may be great in some ways, but when you don't know if you are working from one day to the next or for how long, you can't count on the income which is kind of the whole point, right. But its not just that. You should also continue to look for other things that are better suited for you too. Showing stability in employment can be an important factor, but at this level of employment it is less so. And if you do have another option, you can use it as leverage to discuss obtaining more stability in your present job if you desire to stick with it. Good Luck.

I wouldn't quit the job without a replacement but no harm looking for something better while you continue to work this job.

If you don't get many hours and need more money, look for a new job. God will provide you with a new job when the time is right.

If you're not a full time student or homemaker/primary care giver for someone else, then you'll be better off with something more steady/permanent.

Apply for another job that will fit in.

Seems you are on a zero hours contract which means only used/paid when they need you and not used/paid when they don't, it is also a temporary placement, so you have zero job security, so you stay registered with them and start looking for something with contracted hours and a contract.......you never give up a job without already having another to go to