Creating a form, possible IF query

Right...

I've kinda hit another brick wall with my wonderful checkout holiday tracker...

With some help, we can look-up which weeks are free etc. So now, I need to go to the next step.

What I need to do next is, when a week is closed, set up a message where it says "you must choose another week"

And when a week is open, I'd like it to to set up an input form, where you can enter a name, and the days that they want to book off. Then have this info update on the schedule.

The idea would be that only 5 people can book holiday for each week, so after the 5th person books off the same week, the week automatically becomes closed to all others.

But I really don't know where to start with making forms, or doing this auto-closing function.

The form would need to take in to account

• the colleague's name
• which days of the week they want off
• how many hours each day they have booked off

Can anyone get their head around that for me at all?
Thanks

The most up-to-date copy of the file is attached below