Nothing can be built without a strong foundation. Developing rhythmic sensibilities early on in your music training will provide you with a strong foundation to expand your musicality. Music is a language spoken with sounds, in a specific frame of time. While you need to have a strong command of the sounds you make, of equal importance is when you make them. This is called "keeping time," and is the main purpose of rhythm training.
Having a keen sense of rhythm makes you a better musician in every way. Music is an art that is expressed in real time. The better command you have of that time, the better you will be able to express yourself in it. It allows you to lock in with the musicians that you play with. A strong rhythmic base will allow your melodic and harmonic sensibilities to grow as well. Understanding and feeling rhythm makes playing music that much more enjoyable.
You can approach basic rhythm training in a variety of ways. If you are in music school, specifically a Music University, rhythm training will be a required course, either of its own accord, or as part of the ear-training curriculum. The Internet provides a multitude of beginner rhythm training programs for free and otherwise. It is possible to learn the basics of rhythm through educational books, and most of these come with practice CDs, or software.
In order to understand rhythm you have to know how to read music at a rudimentary level. This involves understanding time signatures, note durations, and other symbols that determine how long a note is played. A basic music theory class will sufficiently prepare you with this knowledge. Familiarize yourself with how beats are counted. In 4/4 time, four quarter notes are counted: 1, 2, 3, 4; 4 beats of eighth notes: 1 &, 2 &, 3 &, 4 &; and four beats of sixteenth notes: 1 e & uh, 2 e & uh, 3 e & uh, 4 e & uh.
In the beginning stages of rhythm training practice reading simple rhythms, tapping them out in real-time with your hands or with your feet. Practice counting the rhythms aloud. If playing an instrument, acquire the habit of keeping time while you play, by tapping your foot. Rhythmic dictation is extremely important as well. This is the practice where a non-melodic rhythm is dictated to you, and you write out what you here, with the proper notation. These exercises should be done on a daily basis, for the best results.
It is highly suggested that you implement the use of a metronome when practicing rhythm. It serves as a guide. The metronome can be set to any tempo, and play the beats perfectly. As you play along, if you speed up or slow down it will be glaringly apparent. It will help you understand what it means to keep time while enabling you to do so.