Types Of Paint               
Always try to use a good quality paint.

Good quality paint gives a much better finish. It covers better and makes the job much easier. It can often mean you don't have to apply as many coats which can save you  time. 

The type of paint you use depends on what you are painting. There are lots of different options so here is a rough guide. 
Walls and ceilings
For walls and ceilings use a Vinyl Matt emulsion . I usually use a brilliant white for ceilings and choice of colour for walls. 
This is water based so clean your brushes with water.

For bathrooms and kitchens you may want something that is a little more hard wearing for which you can use a Vinyl Silk Emulsion. This has a slight sheen on it which make it more resistant to water or grease and is easier to wipe clean.

Most paint products tell you on the tin if it is especially for kitchens and bathrooms.
For woodwork you'll need an undercoat and top-coat . Traditionally these have been oil-based paints, however, you can now get water based paints too. 
Oil-based paints cover well and are hard wearing. The disadvantage is they are solvent based and quite smelly until dry. You will need to clean your brushes with white spirit.

Water based based paints may need more coats to get a good finish and are not as hard wearing. The advantage is they are easy to apply, don't smell as much, and you can clean your brushes with water.
Types of finish

For exterior wood you will usually need to use a gloss finish. For internal painting, most people prefer to use a less glossy or even matt finish which is not so hard wearing but looks good.      
Gloss: Gives you a shiny finish, and is hard wearing and easy to clean. A shiny surface will show up any little imperfections or bad painting.

Satin Wood/ Eggshell: Gives you a mid sheen finish and looks great, but is not as hardwearing as gloss

Matt: Gives a great finish, but marks very easily.
A best practice is to use a gloss for all exterior woodwork and an eggshell for all interior woodwork     
You can buy a paint especially for radiators. Always make sure your radiators are turned off before you begin.
Exterior paint          
For stone work or painted bricks you'll need a Masonry paint. It's a bit like interior emulsion but especially formulated to be hard wearing outside. It's water based so you can clean your brushes with water.

For exterior wood work as a general rule use an oil-based under coat and and an oil-based gloss top-coat.
Just remember that whatever painting job you are doing, always read the tin as it will tell you exactly what the paint is suitable for and how to use it, so follow all the instructions carefully.
And always allow adequate ventilation whilst painting and drying.