We use the present perfect tense to talk about actions that started in the past and are not finished by the time of speaking.

     In the present perfect, we use the word “for” to refer to a period of time, and the word “since” to refer to a point in the past.

Examples:

     –  I have studied English for 4 years. (for + period of time)
     –  I have studied English since 2014. (since + point in the past)

     Use “how long” in present perfect to ask about the duration of an activity.

Example:
– How long have you studied English?

Practice this lesson here: PRPF002.