AddForce instead of modyfing Velocity

I just realized that if i want to use physics with rigidbodies2d i cant move the player or character by modyfing Rigidbody2D.velocity. So how do i do it? Im getting the movement input from GetAxis("Horizontal") and i want the character to move left or right depending on this. Its easy if i want to use velocity but how would i convert this to AddForce?