I echo what full set has said.
Also there are several types of paper.
Laserjet, inkjet.
White paper, clear paper.
Laser jet printers need laser jet paper. This colour is water fast.
I have an inkjet printer. And my experience was as follows
After printing, you need to coat the paper in lacquer before immersing in water, otherwise the ink runs.
Then apply as mentioned above, no problem.
Using the clear paper, light colors are not good on a dark background, the darker colour dominates. Light colours are not effective on dark backgounds but may be fine aon lighter backgounds but expect the base amterials colour to show through.
If planning on using light colours you will need to use the white paper.
Using the white paper, means you will have a white background to your motif. This may be ok but needs planing.
Be careflul with you print layout, otherwise you may use a whole sheet for just a few decals (expensive), you need to plan a little with layout and re-use of the paper in mind. Perhaps always printing at the bottom of the remainder of the sheet, this way the paper can feed through the printer, even if short.
The picture below is printed gold on clear paper. It is shown on a medium blue background. Very disapointing.
The yellow was almost invisible.