Basic Key fittings
Once you have assembled you new clarinet, you need to learn to place your hands in the correct places on the keys and holes in the instrument. As a start, put your right hand thumb under the piece of metal that sticks out of the lower clarinet section. This allows you to hold your clarinet when you are playing the instrument. With the clarinet resting on your right hand thumb, place your left hand thumb on the hole in the back of the instrument. Then take your left hand's first three fingers, and place them firmly on the holes of your clarinet's upper section. Afterwards, take your right hand and place your first three fingers over the three holes on the lower clarinet section. Make sure you have all your fingers firmly in place. If you blow in to your instrument with the correct embouchure (mouth positioning), it will produce the lower G note.
If you take all your fingers off of your clarinet, your instrument will produce a middle octave G. Practice tonguing this note several times before you are ready to move on to the next note.
Suggestions for learning notes
If you are learning to play the clarinet, I would consider in purchasing a fingering chart for the references of the notes on the clarinet. Some notes may not speak because your mouth and your lungs are not yet fully developed. Stick to the middle C, D E, F, G, A, and B if you are just beginning. The G note requires no fingers to play. Practice that note until it sounds reasonable to move to the next. Reading music is also an extremely useful skill, as it widens enormously the range of music you will be able to attempt, as well as allowing the novice clarinetist to use the many printed clarinet tutorial materials available, all of which require the ability to read music. Since the clarinet is most commonly a Bb instrument, the note that is written as 'C' actually sounds as 'Bb'; in the same way, all notes for the clarinet are written a whole tone sharper than they actually sound. This is for convenience in writing, and should not present any problems in practice for the novice clarinetist. However, it is important to be aware that when reading music written for 'C' instruments (where 'C' sounds as 'C'), it will be necessary to transpose.
Also remember to tongue every long note. Keep a good embouchure.