Please inform me on how to make postcards using Libre
SO. . .
what it the postcards used for, and how many prints?
That will help with the correct "how-to" info.
Do you have a template for them?
Are they "specialty paper" from Avery or similar companies?
If you have a specific postcard paper - say two per sheet - then it is better to use the template[s] the paper company should have on their web site.
If you have blank "stack" of postcards, like a package if index cards you can buy in many different places, THEN you need to define the page size to the size of the postcards. No, I do not know what size that is, since I have seem 3 or 4 different size ones that are called "postcards".
Go to Format > Page
The "page format" go to "User" and then set the page with and height, orientation, and margins, to fit your needs.
Or, you might try File > New > Labels
or Templates,
and see if the Avery [or other company's] postcard paper is listed there.
I prefer using the Format Page if I am using paper cut to the size of the postcard, or index card. IF the printer can support the size, then I can format the page to that size.
Then I just fill out the postcard the way I want it to be. I would them create a template file [save as a template] so I can use it over and over again without the need to do all that formatting.
Now, if you are doing some type of Mail-Merge text in the postcards, then you will have to get someone else to help with that. I have not done any mail-merging with LO.
Sir or Ma'am:
The biggest problem that I've seen with creating amateur radio QSL cards is getting the printer to feed the card stock. The dimensions are typically too small for the paper tray and the thickness is too heavy for the paper path.
Your task might well experience the same issues. Of course this reply has nothing to do with the actual question you asked.
I wish you the best.