How to send multi variable information over serial?
You have three options for what you want to achieve (if I understand it right):


Have a fixed length for each variable: If I know each number is going to be two digits, I can send "1234" and the other side can figure out the numbers are "12" and "34".
Have a delimiter character: Have a character that signals a new variable. For example: "213|1234" would translate into "213" and "1234". You could even use the newline character to signal a new line (with Serial.println();).
Do some sort of validation to separate the data: If sending a favorite number and favorite color, I can send "12RED345BLUE" and the other side it can find that it's "12" (both numbers), then "RED" (all letters), then "345" (three numbers), and finally "BLUE" (again, all letters).