it is best to teach it with a native speaker. Now there are many programs and language courses that use this particular technique. You can also learn to remotely by Skype, which is even easier. This is the best known method for me.
There is no guarantee you can.
Every person's capacity to learn is different. Not knowing you it would be impossiblefor a bunch of strangers to tell you that. If you are someone who does learn fairly easily, the speed in which you learn a new language will also depend on if is based in the same roots as your native language. If your native is one of the Romance languages (Italian, French, Spanish, etc), you will more easily learn another Romance language, as opposed to a Germanic (English, Icelandic, Norwegian, etc.) or Slavic language (Russian, Czech, Polish, etc.).
It depends on you. I know some people that managed to learn a language by themselves, but it's definitely not for me. I don't have enough self-discipline, and I need someone to control me. That's why https://livexp.com/skills/english worked the best for me, and with a great teacher, I managed to learn a new language.