Please explain tech.lef , tech.lib
The technology file contains the physical properties of your fabrication process. For example, it would contain the number of metal layers, the design rules, resistances, capacitances, as well as the routing grid needed. This file is specific to the process used, so it would be supplied by the foundry or your gate library vendor. If there are multiple process options (e.g. multiple metal stacks) you would need to select the correct tech file. Usually the file extension for a tech file is .tf.

A .lef (Library Exchange Format) file can contain the same information as a technology file. This can be supplied by the foundry, but it can also be generated from the technology file if you only have the technology file. You can also use a .lef file to store the physical data of a gate or macro library.

Library (.lib and .db) files are usually logical, timing and electrical characteristics of a gate or macro library. These are necessary to synthesize a design, and also necessary for the place and route tool (and static timing analysis in general) to function. These files are provided by your gate library vendor, or the foundry if they supply the gate library. 

These are basically required at the beginning of the place and route phase in order to configure your tool for the process.