Wait for the program to completely finish opening before you attempt to add any music. If the "Copy Files to the iTunes Music folder when adding to library" box is checked, the music will not only be added to your library but also copied to a second location on your computer. You can toggle this option on and off by going to the Advanced tab in your iTunes Preferences dialog box, which can be accessed through the file menu. This allows you to move songs from your computer to iTunes in an easy process. If you're using a Mac, you can find the option by going to the File menu and selecting "Add to Library." If you're on Windows, go to the File menu and select either "Add File to Library" or "Add Folder to Library." The former is for single file use, while the latter is used if you have an entire folder of audio music you want to add to your iTunes library. Find the mp3 files you would like to download from another location on your computer. You can select more than one item from the same folder at once by selecting a song and holding the ‘shift’ key until you have selected the total number of songs you want.  You can add files in AAC, MP3, WAV, AIFF, Apple Lossless, or Audible.com formats. iTunes for Windows can also convert WMA content to one of the above formats when you add it to your iTunes library. Double-click to select it or click on the "Add" or "Open" button in the file window. Because the files you are adding are already uploaded to your computer (as opposed to on a CD), it should take only a minute or less for the music to be transferred to your iTunes library. Go to your iTunes library and scroll to where the imported song/album is located. Check to see that the album info, including the artist, song titles, album artwork, and album name, were all transferred with the music files. If they were not, you can manually add them by selecting the songs, right clicking them, and going to the ‘get info’ button on the menu.

TL;DR in Indonesian:
Bukalah iTunes. Bukalah pengaturan iTunes anda. Temukan opsi "Add to Library". Jelajahi berkas atau folder. Tambahkan berkas atau folder musik. Lihat pustaka musik iTunes anda dan geser ke lokasi berkas yang sudah anda impor.