Actually GPS device will transmit data using NMEA 0183 protocol, with the stated specifications:
Asynchronous Transmission begins with a start bit (logical zero), followed by eight data bits and a stop bit (logical one) added to the end. No parity bits are used. Baud rate=4800 Baud.
My device will transmit the following messages:

RMC Recommended Minimum Navigation Information

1 2 3 4 5 6 7 8 9 10 11|
| | | | | | | | | | | |
$--RMC,hhmmss.ss,A,llll.ll,a,yyyyy.yy,a,x.x,x.x,xxxx,x.x,a*hh
1) Time (UTC)
2) Status, V = Navigation receiver warning
3) Latitude
4) N or S
5) Longitude
6) E or W
7) Speed over ground, knots
8) Track made good, degrees true
9) Date, ddmmyy
10) Magnetic Variation, degrees
11) E or W
12) Checksum

GSV Satellites in view
1 2 3 4 5 6 7 n
| | | | | | | |
$--GSV,x,x,x,x,x,x,x,...*hh

GLL Geographic Position – Latitude/Longitude
1 2 3 4 5 6 7
| | | | | | |
$--GLL,llll.ll,a,yyyyy.yy,a,hhmmss.ss,A*hh

GGA Global Positioning System Fix Data. Time, Position and fix related data
for a GPS receiver
11
1 2 3 4 5 6 7 8 9 10 | 12 13 14 15
| | | | | | | | | | | | | | |
$--GGA,hhmmss.ss,llll.ll,a,yyyyy.yy,a,x,xx,x.x,x.x,M,x.x,M,x.x,xxxx*hh

As stated before, the transmission is asynchronous; so the transmission could start at any field from the described messages.

Initially, I want to catch the $ sign and then using the first message to check the validity of the message, after that I want to extract the latitude and longitude information (Bold and Underlined).

Actually. These messages will be transmitted as long as GPS device is operated. You need only to connect its Vcc and Gnd.

Thanks to all.