The whole purpose of the slant is to have some long-term, stable storage for your yeast. You're right, you don't need the whole thing. You only need an inoculation loopful (not even that really...like 10µL). Use that to inoculate a 5mL culture of wort. Then step that up to 50mL, then 500mL. That way you can get many, many, many uses from your slant. Does that answer your question?