You can start the online installation from the Java download page. If you are using Internet Explorer, the Free Java Download link will automatically detect the browser and give you the correct download link. If you want to download Java for a different operating system, click the All Java Downloads link on the left navigation menu. This is not always necessary, but some firewall setups will block the installation of Java. If this occurs, then you will need to disable the firewall. The procedure for disabling a firewall varies depending on your network configuration. Open the installation file that was downloaded from Java. Confirm that you wish to install it by clicking the Install button. Java comes bundled with other software. During the installation process, you can choose whether or not you want these installed. The program will prompt you to confirm the completion of the installation. You will need to restart your browser in order for Java to begin working.

TL;DR in Indonesian:
Unduhlah peranti lunak Java. Blokir dinding api (firewall). Jalankan program pemasangan. Lakukan konfirmasi untuk memasang program pihak ketiga. Selesaikan pemasangan.