After you have finished the installation of your first piece you can purchase installing the other parts to make the system complete and also, install the downspouts.
So, you will need to join the pieces together by 4 inches and apply sealant to fix them together. Also, you will use screws for a better joint which will be placed on the sides of the gutter.
You will need to have already the angle of 45 degrees if you want this job to be easy. You will apply sealant on the connected pieces and a corner joint over them. You will also use screws placed on the sides.
Next, you will have to install the downspouts by placing a sleeve at every point where a downspout will be placed. You will fix the sleeve with sealant and screws. After you make sure that the sealant is completely dried, you will install an elbow which will be angled toward the house. Then, you will have to install the other elbows which must be perpendicular to the house and as flush as possible to the house.
Now, you can install your downspout and you need to take care of its length. It should be about 6 inches above the ground level. You will join it with the second elbow and you will attach at the bottom of it an elbow which will carry the water away from your house. After that, you will need to secure the downspout by fixing him to the wall using metal straps which should be placed 5 to 8 feet distance between them. Now, your system is complete and you can check if it’s working properly.