If you are new to VMware certification, the first requirement for VCP6.5-DCV certification is to gain experience with vSphere 6.5 (the certification guide suggests a minimum of six months).
There are different ways to practice using a product: studying it, working on it in the field, and using labs.
Also, if you are new to VMware certification and this will be your first VCP, one of the mandatory requirements for VCP6.5-DCV certification is to attend at least one of the required training courses at a VMware Authorized Training Center (VACT).