First, you need to get an idea of karate as a sport and means of self-defense. Check out the Internet thematic websites dedicated to different styles and schools of karate. Select the most suitable direction. And also remember the ones that you absolutely do not fit (for example, the direction of Kyokushin is considered the most difficult and toughest of all areas of karate).
Further, when you have decided on the desired styles, you need to choose partition. View ads local sports schools. They are constantly there is a set of groups as beginners who want to learn how to fight and more prepared athletes who want to raise the skill level. Or, if you have heard of a particular section in your city, or karateschool with good reviews, ask there. If the result is worth it and the classes will be fun, it is better to spend the extra time on the road.
Before you make a final decision, be sure to check with a trainer ( karate-schools coach called "Sensei"). Be sure that you have had a good relationship with your future mentor. Only an experienced Sensei will be able not only to supply good karatetechnique and learn to fight but to raise morale.
Once you start training, don't forget to continue self-education. Watch themed movies dedicated to the great warriors of karate, the founders of karateschools, as well as paintings, raising the spirit of war. Ask your Sensei to recommend you some literature dedicated to martial arts in General and karate in particular. And don't forget to devote time to General physical preparation. Without a good physical shape not be able to master the basic techniques of karate and to learn how to fight well.