Kindly Assist in Understanding the Below Irule

Allow me clean that up a bit:

when CLIENT_ACCEPTED { 
    set default_pool [LB::server pool] 
}
when HTTP_REQUEST { 
    check for pages needing to not redirect to https 
    switch -glob [string tolower [HTTP::uri]] { 
        "/getxsl.asp*" { pool $default_pool} 
        "/radsomsgreceivertri.asp*" { pool $default_pool } 
        "/radsofiletransfer.asp*" { pool $default_pool } 
        "/reader.sod*" { pool $default_pool } 
        "/clockserver.asp*" { pool $default_pool } 
        default { HTTP::redirect "https://[HTTP::host][HTTP::uri]" } 
    } 
}

Is the above irule stating: HTTP to HTTPS redirect except the extensions: /getxsl.asp,/radsomsgreceivertri.asp,/radsofiletransfer.asp,/reader.sod,/clockserver.asp ??

The answer then would be yes. If the request URI matches any of the defined URIs, traffic will proceed to the GUI-defined pool. If it doesn't match anything, it will fall through to the default condition and redirect to HTTPS. I tweaked it a little bit though. You're using a -glob switch but not defining any glob conditions, so while it would match "/getxsl.asp", it would not match "/getxsl.asp?". Adding the star character at the end allows the URI to grow.