The [read -resize $1 mysound( should is actually what pd calls a message. You can send all kind of messages to all objects to do things. In this case it is a message sent to the [soundfiler] object and contains instructions for that object. It is interpretted as follows :
read : tells the soundfiler to... read a soundfile (there's also a write)
-resize : this flag tells the soundfiler to resize the table it will read the file into
$1 : this is a parameter from the message and is actually replaced by the output of the [openpanel] object => it will contain the full path of your selected file
mySound : this is the final parameter and is the name of the table
The [;mySound write sound.txt( is a kind of special message you can perform on tables. It just instructs the table to write its contents to a specified file.
Remember that you can almost always right click an object to request its help file and further I can recommend you to read the patches from the help browser (2.control.examples/15.array.pd and 16.more.arrays.pd will show you what's possible with tables).