If you use the 'Write' commands other than 'WriteLine', it outputs the values as binary (not human readable and generally less space used).
To read them back you use the 'Read' commands. They need to be read using the same type as written and in the same order. If you use a WriteByte and WriteFloat and then try to read using ReadInteger and ReadFloat, you won't get the correct values.
And the extension of the file has no meaning at all for AppGameKit (at least it shouldn't).
If you did want it to be all human readable then you use only the WriteLine command and the Str command to convert numbers to strings before you use the WriteLine. And then you read it back with ReadLine, storing it into a string variable, and do any conversions on the results that you want.
Cheers,
Ancient Lady
AGK Community Tester and AppGameKit Master