there are two kinds of flow :
1. Flat flow - this flow u dnt find hard macros, so no need of partioning. The design is realised by using only standard cells.
2. Hierarchical flow - this flow includes macros, making partioning necessery. The design realisation includes Standard cell as well as macros.
Flat flow: this includes the fallowing steps,
1. intial step -init 2. Placement step 3. Prects step 4. CTS step 5.Post CTS 6. post CTS_hold 7. Route 8.Post Route 9. Post Route_hold 10. post Route_di_hold 11.post Route_si 12. Sign-off.
Hierarchical flow: this includes all the above steps along with partion before initial step & assemble after sign-off.
You can find more information in the help option available in the tool