hi,
SDLC- Software Development LiFe Cycle
it contains 6 Phases
1)Gathering Software Requirement
2)Software Design and Analysis
3)Coding
4)Testing
5)Implementation
6)Maintainance 
in every phase Software Tester is involved.
In First Phase SRS ( Software Requirement Specification
)document is Craeted and Validated.

In Second Phase Design / Algo are Analyze and design
document are craeted by design team which is tested by Tester.

In Third Phase Coding, which is done Software Developer are
checked taht all path are covered are not, coding should be
done in such a way that new changes are made easily, and
application should be user friendly.

in Fourth Phase Actual testing ( Unit , Integration,
System,UAT) is done.

In Fifth Phase Check that Application is working fine in
Different OS environment

In Sixth Phase Configuration management is done..

in this way Software Tester is involved from beginning of
Any Project.