Article: The easiest way to do this for Minecraft is by double-clicking the Minecraft launcher and waiting for it to update itself if necessary. For Java, open Internet Explorer, go to https://java.com/en/download/installed.jsp, click Agree and Continue, and follow any on-screen prompts.  If nothing happens, your Java is up-to-date. Since most modern browsers don't support Java, using Internet Explorer is the best way to ensure you don't run into any errors. The Java Development Kit (JDK) is necessary both to run Tekkit's launch file and to use Minecraft Forge later:  Open the JDK website  Check the "Accept License Agreement" box in the "Java SE Development Kit 8u171" section. Click the jdk-8u171-windows-x64.exe link to the right of the "Windows x64" heading. Double-click the downloaded Java file, then follow the on-screen setup instructions. Go to https://www.technicpack.net/modpack/tekkit.552560 in your computer's web browser. It's a blue button in the lower-right side of the page. Right-click the Tekkit ZIP folder, click Extract All... in the resulting drop-down menu, and click Extract at the bottom of the pop-up window. You can change Tekkit's memory allocation by doing the following:  Right-click the launch file. Click Edit in the drop-down menu. Review the "-Xmx[number]G -Xms[number]G" values:  The first number refers to the maximum number of gigabytes of RAM your server will use. The second number refers to the minimum RAM your server will use.   Lower or raise the numbers to reflect your computer's specifications if necessary. Double-click the launch file to do so. This will open a Command Prompt window in which Tekkit will begin running your server and unpacking its necessary files. You will have to click Allow access if prompted by Windows Firewall to allow the program. Once your Command Prompt window finishes loading information, you're free to proceed with the next part of the setup process. You can close the server by typing in stop and pressing ↵ Enter.

What is a summary?
Make sure that you have the latest version of both Minecraft and Java. Install the Java Development Kit if you don't have it. Open the Tekkit download page. Click Server Download. Extract the server folder. Change Tekkit's available RAM. Run the Tekkit installation. Wait for the Command Prompt window to stop loading information.