How can I write to a professor for introducing myself?

Do you have his email or regular mail address? If not, you can probably find it by looking up the website for the place where the professor works.

Once you have that, the rest would be pretty straight forward in expressing your interests and asking any questions you might have.

If you can't find a specific name, you could send it to the professor in care of the department and place of employment.

It would be helpful to know also why you are wanting to write to a professor in order to introduce yourself. Perhaps you are also wondering what to say?