Computers aren't very smart. Sure, they can do a lot of math or help you search the Internet. But, if you asked a computer to vacuum the house for you, could it do it? If you asked a computer to draw a picture of a bird for you, would it? A computer would have no idea about what you're saying.
Computers are bad at understanding things. If you don't give them exact instructions, they become confused and make mistakes. Telling a computer what you want it to do is sometimes hard because you have to explain things very carefully.
Because computers don't understand English, you have to give them instructions in special computer languages that computers can understand. This website will teach you the JavaScript language. Most computers understand the JavaScript language.
Don't be frustrated if you write some JavaScript that a computer doesn't understand. Remember that computers are easily confused, and all the JavaScript instructions have to be exactly right. Computers are very picky! Little mistakes or problems in the JavaScript are called bugs. Even the best programmers make many, many bugs.