What is
so and sth (something)????
Please don't use text messaging abbreviations when asking a question. 
1) to apply for / 2) to so. / 3) sth.
1) make an application for; He applied for a loan;
2) apply to the university for admittance to the program
3) put on; apply makeup to the face
also, "apply yourself" which means to try your best, make an effort to do something to the best of your ability.
1) to be true of so. / sth.
1) it must be "to be true to"; faithful to
2) to be aimed at so.
???
3) to hold true
to last, honor; respect; The colors held true on that old quilt; He held true to the wedding vows
4) good for so.
4) good for something? - fits, works, This hat is good for gardening.