PRESENT PROGRESSIVE — what's happening right now, while he's talking
You already know estar. Now he sticks a verb on the back of it and you've got the present tense people actually use. Trabajo — what I do with my life — versus estoy trabajando — don't talk to me right now. The whole rule is -ando, -iendo, plus a short list of irregulars that trip everybody: dormir → durmiendo, decir → diciendo, pedir → pidiendo.