char buffer; //This is where the data will be merged into. Ideally you should make this as small as you can whilst still having enough room
sprintf(buffer,"1 %ul %d %d %d %d %d", millis(), distance, pressure, prSwitch, Fldtemp); //merge together
Basically sprintf has a set of special characters (the %_ where the _ is a letter(s)). As it works along it replaces each of these with the corresponding variable (first % is the first variable, second % is the second variable and so on).
Each of the special charaters formats the variable in a different way. For example %d takes an integer and converts it to a string of numbers. %c takes a byte and prints the corresponding ascii character (so 30 would print ' ' (space)). %ul takes an unsigned long type (which is why it is used for millis()).
There are others as well, you would have to look on the cplusplus reference (if you google sprintf() you should find it).
Note that in my example as I don't know the variable types of your numbers I have assumed that they are all bytes or integers (so %d) except for millis() which I know returns an unsigned long.