If just one of your outlets has stopped flowing - perhaps just the sink, then it is likely that your drains aren't blocked and it is just a U bend or other pipe that has a blockage.
Blocked Sinks and baths
These are possibly the easiest to clear. Under your sink there should be a 'U' shaped length of pipe. This is used to collect a small amount of water that acts as a trap and stops smells coming into your home through the pipework.
Sometimes this can get blocked by a build up of vegetable matter or other solids.
Simply unscrew the joints to the u-bend and clear the blockage - be sure to have a bucket or some other container underneath when you disconnect.
A plunger might do the job just as well!
The same kind of blockage can occur with baths. If your washing machine is plumbed in, a blocked u-bend might also stop it draining.
I know its the drains
What follows is not advanced drain cleaning advice.
Clearing my blocked drains.
In just about all cases of DIY drain cleaning you will need a set of drain cleaning rods.
Also you should buy a pair of sturdy rubber gloves and ideally, eye protection.
Next you need to identify the manhole cover that provides access to the drains.
When the manhole cover is removed, take care that nobody else approaches the opening, it is a hazard, you are responsible for keeping the area safe!
With this removed, assemble two or three rods along with the 4" rubber disk. Insert slowly into the drain so that the rubber disk penetrates two or three feet - this may require the addition of extra lengths of drain rod.
This should be inserted in the direction of the property, if you are on mains drainage, most likely away from the street.
If the access point is backed up, then you should clear towards the street.
You might have to feel - or probe - for the drain hole when inserting the rods if it is obscured with effluent.
Take care when adding or removing drain rods.
With the rubber disk and rods in the drain, very quickly pull the rods out - this is often sufficient to start the drains flowing.
If the drains do not flow, try again but with more lengths of rod inserted.
From here on in the best advice is trial and error.