Find it in the the applications folder of the Finder, and double click on its icon.  From Selection will turn your cursor into a reticle. Click and drag across the rectangular area you wish to capture.      From Window will turn your cursor into a camera icon. Highlight the window you want to capture and click.      Entire Screen will start a countdown. Arrange your screen how you want it captured and wait for the timer to run down.    The screenshot will immediately open up as an untitled Preview image window. Open the file menu and select Save. Type a name, select a location and file type, and click Save.

TL;DR in Indonesian:
Buka Preview. Buka menu File dan gerakkan kursor Anda ke Take Screen Shot. Pilih "From Selection", "From Window" atau "From Entire Screen. Simpan gambar baru Anda.