what are differences between PVST and PVST+?
Here's an excerpt from the link below. Just go through the document and hopefully it should clear all your doubts.
In order to support the IEEE 802.1Q standard, the existing Cisco STP implementation was extended to become PVST+ by adding support for tunneling across an IEEE 802.1Q mono Spanning Tree region. PVST+ is therefore compatible with both IEEE 802.1Q MST and Cisco PVST protocols and does not require extra commands or configuration. In addition, PVST+ adds verification mechanisms in order to ensure that there is no configuration inconsistency of port trunking and VLAN IDs across switches.
These are some operational highlights of the PVST+ protocol:
PVST+ interoperates with 802.1Q mono Spanning Tree through the so-called Common Spanning Tree (CST) over an 802.1Q trunk. The CST is always on VLAN 1, so this VLAN needs to be enabled on the trunk to interoperate with other vendors. CST BPDUs are transmitted, always untagged, to the IEEE Standard Bridge-Group (MAC Address 01-80-c2-00-00-00, DSAP 42, SSAP 42). For completeness of description, a parallel set of BPDUs are also transmitted to the Cisco shared Spanning Tree MAC address for VLAN 1.