What do you not understand about what you've already read on the subject? There's no point our repeating what you've already read and failed to understand. If you haven't read anything yet then that's your issue. Do appropriate research for yourself first and then come back here if you have specific issues.
If I take an Example to explain you. When we make a building, we need a design/Blueprint/Architectural plan then we make the pillars, wall etc.
Similarly to develop a website we have to decide how many pages you want in a website and suppose in Homepage where you have to put LOGO, Social media buttons, where you have to place content, How many images you want to add and where you have to place that images.
This will help you to save your time, Money and effort.