If you don't have a sifter handy, you can use a strainer to sift your flour. Find a strainer large enough to hold the amount of flour you need to sift. Find a bowl slightly larger than the strainer, as you'll be holding the strainer over the bowl. Take the strainer with one hand as you pour. Make sure to position the strainer just over the bowl you're using to collect the flour.  Flour is a powdery substance, so it can be a bit messy. Make sure to pour slowly. If you pour too fast, the flour may get on your shirt and your work surface. It's a good idea to wear an old shirt or an apron when sifting flour. Be gentle as you tap. You should tap with one hand, and hold the strainer with the other. Your tapping should cause flour to lightly sprinkle out of the strainer and into the bowl. The flour should be thinner and lump free as it falls into the bowl.  If the flour still has lumps in it when it falls in the bowl, you're tapping too hard. Put the flour back in the strainer and start over. It may take awhile to get all the flour through the strainer, so have patience. Do not tap the strainer hard to speed up the process. If the flour goes through the strainer too fast, it may not be sifted thoroughly enough.

TL;DR in Indonesian:
Siapkan bahan-bahan yang diperlukan. Tuangkan tepung ke dalam saringan. Ketuk ringan sisi saringan sampai tepung habis.