I have a 'folder Creation Failure' so I can't export. what did I do and how can I fix it so I can export pictures again. please.

It is possible you have a particular destination folder remembered within your Export settings, which no longer exists physically. In this circumstance, LrC obviously cannot proceed.

Two places this destination folder may be remembered: 1) at the top of main part of the Export window, you have selected to export to a chosen folder - 2) this destination has been previously saved into a named Export preset.

One way to resolve is to update the remembered destination folder to something which does exist - in the dialog, or by updating export preset(s).

This applies whether you are exporting direct to this place, or are exporting into a newly made subfolder of this, as defined in the Export settings.

Another way is to change the destination type menu (at top of the Export window) so that instead of repeating a previously remembered location by default, LrC will instead ask you each time.

​@anneh91370696  Are you talking about Lightroom Classic (LrC icon) or Lightroom (Lr icon)? Please tell us the version NUMBER (we need the version NUMBER and not words like ‘latest’ or ‘up-to-date’). What is your operating system version NUMBER?

Please tell us the exact steps your followed, in detail, leaving nothing out, be very specific; and please tell us the complete exact word-for-word error message.

Reinstall will not cause your pictures to be lost, and most likely will not help anyway.

Unfortunately you haven't given us a detailed dwscription of your issue and any information about your system. Therefore, all proposed solutions are a look into the crystal ball.

Which folder do you have deleted?

Which operating system (incl version) and which version of Lightroom do you use?

Please provide a copy of your 'System Info'. This can be get from the LrC Help > System Info menu item. There's a copy button in the System Info dialog. Press this button and paste the info into your next forum post.

Do you have the appropriate write access rights to the location in which you like to create a folder and export your images?