Get a rose head watering can - the kind that has a flattish pad on the spout end with lots of tiny holes in it. Then you water from above, which will take longer to do properly, but a) you won't disturb the soil at all, and b) it'll be like rain falling, which is natural, and c) the roots will get the aeration needed and used-up chemicals will wash away properly. Submersion is only in cases of dire emergency - i.e. you come back from holiday to find your tree totally dried out by mistake. What also makes a difference to doing it right is if the soil has a lot of grit and/or perlite in it, so it drains very quickly, but don't let the pot sit in the drain water (or roots can rot), but keep it above it on stones that are in a wide 'humidity tray' underneath, also kept full of water, just below the stones' tops.

thanks so much. i just wanna do a good job

Bonsai watering can be tricky. I've heard the submersion technique a lot. What I have found is that this should only be used in emergency situations if you are using a clay soil that has dried out to a point where is is hard to rehydrate using the rose head method described above.

Also, I'd recommend a humidity tray. I generally only have to water my fukien tea once a week but I keep the tray underneath it filled with water to give it humidity and its doing great.