First of all cool the wort, the beverage being measured, down to approximately 60 degrees. However, if you think the temperature of the liquid is above or below 60 degrees, then you will have to adjust the calculations. Remember to take your time to make sure that beverage has properly cooled and it is at the desired temperature. Make sure to constantly check the temperature to make sure.
Take a long narrow container like a test tube or test vessel and pour the wort into it. Be careful to not overfill the vessel as the liquid might spill over the rim.
Now, place the beer hydrometer into the container containing the wort and then carefully twist if for 4 to 5 times, using your fingers. This simple activity helps in popping the minor air bubbles that were collected all around the hydrometer. Make sure that the bubbles are completely gone from the end of the beer hydrometer.
Grab a pen and writing pad and simply record the number at the surface of the wort on it. Now this reading will tell you the whole story behind the fermentation process that how far it has gone and when it has stopped. Make a record of this information as you will need it to finish or update the fermenting process of the beer.
This is how you have to use the beer hydrometer. Do not throw away the readings as you can use them for future reference while comparing the samples.
You can get expert advice online when it comes to using a beer hydrometer from various websites. There are many small or medium sized brewing companies that have provided plenty of information for those that want to brew their own beer properly. Although it can be time consuming but it is an interesting hobby that many do to earn money.