Just paste this in your Remote tab in mIRC.
on *:text:Whatever text you want here:#channel: {
.notice $nick Insert your message here
}
Instead of notice, you can also use
/msg nickname message
Sends a private message to nickname without opening a query window.
/notice nickname message
Sends a private message to nickname without opening a query window for either you or them.
/query nickname message
Opens a query window to this nickname and sends them a private message.
EDIT: If you want to send a message to yourself, instead of $nick you want your own username there. $nick will send a message to the person saying the text specified in the on text.
Since you're a new scripter, I suggest reading through the help files whenever you can and read up on the context provided on the forums, they can push you a great distance on the way to where you wanna be.
My most important tip is to remember to always close your brackets, ALWAYS. I can't tell you how much I've been screwed from forgetting one } in my code.