How to start testing using automation tool? What will you do first? Will you directly automate the testcases or what you do before using automation for your project??

The first thing you need to before you start writing your scripts is to
Create a Testplan then
1) Create a framework
2) You can either record it and edit it
3) or You can develop it from scratch.
4) If you're using Silk Test then using multitags for object idenntification is good.
5) Multitags are 0f 6 kinds - Caption, PriorText,Window Identifier, Index, Attributes, Location
6) You can go for single tag also provided you negotiate with your dev team that this tag is going to be the standard tag across the builds.
7) Location and Caption tags are not very reliable. For eg, for dynamic windows it keeps changing. There is a simple way to overcome it though.
8)Then you can start writing your testscripts (testcases). Consider what testcases are repeatable across builds and start automating the testcases.
9) Start defining your Global methods and functions in your frame file.
10) Have a Constants file also ready where in you can define all your application constants.