There aren't many choices when shooting with a Holga. There are two apertures, sunny(f/11), and cloudy(f/8), and two shutter settings, 1/100, and bulb. There are also some some symbols that can be set for the focusing distance. The advantage some claim for the Holga is that its simplicity allows a photographer to concentrate on just taking pictures. The pictures the Holga takes are known for some sharpness at the center that becomes soft at the edges. Also vignetting and light leaks are considered a feature in a Holga.
I am one of those who does like what the Holga can do to an image. I don't see myself ever using one frequently, however every few weeks I get the urge to see what results I can get.
I took the one above last summer holding a yellow filter over the lens.
This one is from one of the few snowfalls here this winter. While shooting this roll I again learned the lesson of making sure that the shutter setting is on N and not B. At least on my Holga it is easy to switch the setting to the bulb setting which results in some blurry images. I remember checking the setting before I started to shoot, however I must have pushed it over by accident and it ruined my first 8 shots.
You can take either 12 6X6cm images or 16 6X4.5cm images with a Holga. To do the 6X4.5cm you need to add a mask. The first time that I used color film in the Holga I had the setting to 16 images, however I forgot the mask. I still liked the results.
There also is a fish-eye attachment for the Holga. I don't care for this much and have only used it once.
Lastly, it is fairly easy to run 35mm film through my Holga. I can fit a regular 35 container in there and count the turns to get the spacing right. I forget however many turns I used - so it isn't something I have a lot of enthusiasm for. Also if you do this you need to tape up the red window and unload the film in the dark.
So that covers my Holga experience to far. If you are interested, a search will turn up so much information on the Holga that you could probably spend a day reading about it. Still since a Holga is cheap probably the best way to satisfy any curiosity would be to get one and take some pictures.
As usual there is a Gallery.