All you need for this DIY is:
A cardboard box or piece of cardboard big enough for the letter you want to make.
Start by drawing out your letter, I’ve seen templates for giant letters online but I think it’s pretty easy to do free hand. You need to draw it wide enough for the flowers to stick onto but not so wide that you have cardboard showing through. Mine was a couple of inches wide all the way around.
Once you have your letter all cut out you can heat up the glue gun and start sticking your flowers on. You could arrange them before hand or just wing it like I did. I like the way that mine aren’t in a particular pattern but just do whatever you think looks best. The flowers that I used had quite protrusive plastic stems on the back of them so I just cut these down so that the flowers didn’t stick too far out from the cardboard.
If you are using different sizes of flowers, stick down all the bigger ones first and then use the little ones to fill in the gaps and hide any cardboard edges that you can see.