The AT89C2051 Micro-controller follows the 8051 Architecture. It has a USART port that can be used for serial communication. Both the GPS module and GSM module works with serial communication. 

You simply have to connect the Rx and Tx pins of the MCU with GSM and GPS moudles Tx and Rx pin and write a program for data transfer. Details on how to program the AT89C2051 for USART can be found in its datasheet. 

But if you are a beginner then you can refer to this link below

https://circuitdigest.com/microcontroller-projects/gsm-module-interfacing-with-8051-at89s52

Where you find how to program for serial communication in 8051 architecture. The program will almost be same for AT89C2501 except for some register name which you can find in the datasheet. Once you know how to interface the gsm module the GPS module also follows same procedure