The difference is in form, for example, to know, knew, is known, want to know, don't know, etc. 知る is the original, basic form and we usually change it when making a sentence. わたしは日本を知っている = I know Japan. わたしは日本を知りたいです = I want to know Japan. わたしは日本を知りません = I don't know Japan. わたしは日本を知りませんでした。=I didn't know Japan. あなたは日本を知っていますか? = Do you know Japan? 日本を知るための機会 = an opportunity to know Japan

Karol, thank you so much for your explanation , it's so helpful

Thing is the verb 知る describes a change of state (the act of learning new knowledge) rather than the state of knowing something. And the ~ている form is exactly what you need to use with a verb describing a change of state in order to indicate the continuation of that state. So 知っている means having knowledge about something, whereas 知る means acquiring that knowledge. Also remember that in Japanese the present tense and the future tense share the same verb form and actually when I see the verb 知る without any context, I associate it with future tense rather than with present tense. 2 simple examples to illustrate my reasoning: 知ってる？ ("do you know?"); いつ知る？ ("when will you know?). Hope this helps :)

Masaya , ありがとうございます, that was so much help