HSERIN [WAIT("**play#")STR data\6]

wait for **play# then then next 6 characters will be present in data, well I wish, I get an error with syntax

ERROR Line 59: Expected ']'.
you're really close!!! just a ',' is missing + array variable definition

Code:
    ' Variable Definition
    ' -------------------
    SerData     var   byte [6]
   
Start:
    ' Program begining/Main Loop
    ' ==========================
    '


    HSERIN [WAIT("**play#"),STR serdata\6]
    hserout [str serdata\6]
    goto start
the above will echo you the next 6 character next to your **play#

Also I read in the manual STR ArrayVar\n{\c}
Receive string of n characters optionally ended in character c

Does this mean I dont have to specify the value of n

HSERIN [WAIT("**play#")STR data\n\"!"]

wait for **play# and copy the next characters upto the ! to data.
nop ... wait for **play# and copy the next 'n' character or previous ones if the last one is '!'.

must be write HSERIN [WAIT("**play#"), STR lala\n\"!"]

Hope I am not imterupting you steve with all these questions.
Since i answer to this... no. Don't be afraid. We're all here to learn/help as we can.