Rotation of 3D vector about X-Axis and Yaxis

Hi,
In the following link i cant understand the angle A which is defined as angle of V with respect to X-axis.

https://www.siggraph.org/education/materials/HyperGraph/modeling/mod_tran/3drota.htm
This means i cant understand following two things:

1. How to rotate V about X axis to put V in XZ plane

and

2. How to rotate V about Y to align it with Z axis.

Some body please guide me.

Zulfi.