As an indoor gardener, you'll need an indoor gardening water dispenser of some shape or form. The dispenser you choose will depend on a number of factors, including:
Most beginner indoor gardeners will use an ordinary watering can. This is perfect for most people who have a couple of smaller plants scattered throughout the house. Smaller watering cans are generally more suitable for indoor use and their narrower spouts give you more control in directing the water where you want it. The last thing you want is to miss the little pot and splash water all over the place!
So, you definitely need a small watering can, if nothing else!
If you've got plants that like higher levels of humidity, you'll need some way to elevate the humidity in your house. A spray bottle or mister is one very effective way to do this. Raising the humidity is especially important if your house is heated, because heating tends to dry the air.
Watering becomes a bigger job if you have lots of plants. For example, if you have a grow room filled with dozens of containers. If you have a grow room, you may want to look at an indoor garden hose or a fully automated watering system, depending on what your budget allows. Fully automated systems can be surprisingly affordable if you go for one of the simpler systems. I recently purchased a little gardener computerised timer, piping and risers for under $50-$60. And it works a treat so far.
An automated watering system or self-watering probe is also great as a vacation watering system. If you spend a lot of time away from home, your plants will really appreciate one of these!
It can be a pain in the neck to water larger, thirstier plants with a small watering can. Rather use a larger watering can or indoor garden hose for these.