As a graphic designer you need to be able to show potential customers what you can produce. It may be that you have no qualifications relating to design work and therefore the only thing that potential customers have to go off is your previous works.

When creating a portfolio try not to just stick a random load of logos, flyers and website designs in to a folder as over time you will start to forget what the brief was and it can also look messy to a potential client.

When putting your portfolio together do a brief few paragraphs talking about the brief for the project. You may want to show a previous logo the client had used and discuss why they wanted to change it, then state what you did (that is within the brief) that created the final artwork.

Remember to update your portfolio as often as possible to showcase your latest work.