Either way the gutter brackets should clip around the top of the half round gutter length to hold it securely in place.
How to install gutters on a metal roof.
Crimp one end of the short length of downspout with a special sheet metal crimper.
If you are using metal materials you may need to slide the gutter into the gutter brackets from the opposite end.
For self assembly the easiest way is to use a suspended type of structure which provides for fastening the gutter to special hooks located along the eaves.
This option is preferable since wall gutters that are used on seam roofs are the task of professionals who cover the roof of the house.
With the three blades on the inside of the tube hold the crimper against the inside corner of the tube and squeeze.