Firstly, there’s the plain/polite form of speech called “teineigo” which is principally determined by the absence or use of desu and masu. This is the Japanese you generally learn in text books and at private colleges. Secondly, there’s the use of humble and honorific forms of speech, called kenjyougo and sonkeigo respectively, when dealing with vast social status differences between the speaker and listener or speaker and subject. These two ‘degrees’ are independent of each other, in that one can be plain humble or humble polite, as well as plain honorific and honorific polite, should one want to explore the full range of options.

How and when to talk plain or polite, and when to be humble or when to be honorific, depends very much on the concept of in and out group, as well as familiarity. In ones familiar in group, one can talk in a plain and informal manner, while talking to someone who is part of ones formal in group, or part of an out group, typically warrants polite speech. When one talks to someone in ones out group that is of clearly higher social status and you wish to acknowledge this fact, humble and honorific speech is typically used as well as polite form.

As a non-native speaker there will be no expectation of you to speak polite Japanese, by Japanese. However, when you first met Japanese they will most likely speak to you using polite Japanese. In particular, phone calls and talking to staff in any customer service role you will find particularly difficult. You will be lucky if you understand anything at all.

As a beginner you will only want to concern yourself with teineigo – the use of desu and masu. Unless you intend to go to Japan for business and are determined to speak Japanese while doing business then I wouldn’t worry about learning kenjyogo or sonkeigo for the time being.