Pretty basic & easy to fit mate, fix the mounting bracket to the camera first this gives you something to hold onto and I always tape the PTZ ball so it don't move while I am installing it ( Do NOT hold it by the cable ) I use the PFA120 Junction box fitted to the outside wall and it comes with it's own gasket and 4x 8mm Hex Bolts & Allan key tool included.
1 person should easy be able to fit it via holding onto the bracket with one hand and doing the rest with your other hand obviously being careful if at the top of the ladder 20ft up
. You should already have your RG45 lan cable in the back box via the 20mm cable gland to weather proof it and just enough sticking up through the back box to connect the camera's end.
Make sure that the Rubber gasket is seated proper before you mate the camera to the backbox as you don't want to damage it.
What I will say if you don't feel confident then get a friend and another ladder.