A gallery is a grouping of images, usually with captions. It’s requires the least amount of sequencing (since visitors to your portfolio will be able to pick and choose what order to view the images in), and can give you the most opportunity for showing detail in images. Once they visitor clicks on the image, they can move through them in the sequence you’ve specified.
Here’s what a gallery looks like (be sure to click on a image for the full experience):
Galleries like this are a standard feature of WordPress. WordPress.org has great instructions for creating galleries on their site at this link.