I am having trouble assembling a component around a custom axis, i have created an axis through two points and i wish to mate a cylinder in a concetric position on the axis.
I am having trouble selecting the axis.
I am new to fusion 360 any help on the matter would be appricated 
It would be much easier to explain if you could share a screenshot, a screencast or even better, share your project/file. You can export the fila as an .f3d and attach it to you next post.
In Fusion 360 an axis has an infinite lentgh and as such has no center and end points. What you can do is create a sketch with a line along that axis and then use a revolutte joint between the cylinder and the line.
Yes, as @TrippyLighting says, it would help a lot if we knew more details about what you are trying to do. However, I can make a guess. I assume that you have two components. One component has an axis in it. The other component has some cylindrical geometry. You want to create a joint between these two components, so that the cylinder in the second component is aligned with the axis in the first component.
Today, in Fusion, you can not do this directly. The Joint command does not allow selection of work geometry for the joint origin (connection point). However, you can sort of achieve this, with some limitations. The Align command does allow selection of an axis. So, you can Align the components, then create an As-Built Joint with the components in this orientation.
Here is a screencast showing how to do this:
Is this somewhat close to what you are trying to achieve?
Jeff Strater (Fusion development)
