As long as = So long as = During the period that (showing Time) – जब तक
As far as = So far as = Upto = To the extent that (showing Distance) – जहां तक

Examples

As long as we are alive, we have hopes. (जब तक सांस है तब तक आश है.)
As far as I am concerned, I am not going there. (जहां तक मेरा सवाल है मैं वहां नहीं जा रहा हूँ.)
She was wearing the skirt as far as her knees. (वह घुटनों तक स्कर्ट पहनी थी)

जहां तक तुम्हारी नजर जा रही है वहाँ तक मेरी जमीन है – Only my land is there as / so far as you see.
यह रास्ता मेरी गाँव तक गयी है – This road extends as far as my village.
जब तक मैं यहाँ हूँ तुम्हे चिंता करने की जरुरत नहीं है – As long as I am here, you need not worry.
जब तक बिजली है तभी तक हमलोग पढ़ पाएंगे – As long as electricity is there, we will be able to continue our studies.