Planning is definitely one of the most important stages in designing a website. Most of the work boils down to knowing exactly what and how you will design and develop your website; planning is where all these decisions will be made.
You need to first define your target and your website objective, what you want to achieve, and for whom. Imagine that you're creating an online e-commerce website for a gadget company. The objective will be to sell those gadgets online (the "what"), and the target would be men of the age group of 25 to 50 (the "who"). These are usually pretty simple to understand. However, in case you ever find yourself with an unclear briefing from a client, make sure that you understand their objectives and targets beforehand, because there's nothing worse than an uninformed designer working on a project.
However, in this case, we're creating our own portfolio page. So, essentially, we're creating a page intended to showcase our work (the "what") to designers...