Female cuc (as with squash , pumpkins etc) have a small cucumber just behind the bloom. The "stigma" is in the center awaiting pollen.
Male cuc bloom just have a stem attaching the bloom to the plant. The "anther" has pollen on it in the center.
I use a small soft paint/artist's brush.
I get some pollen on the tip of the brush from a male, (you can see a yellow dust on the tip of the brush if you look close, (I need to have my glasses on) )
& transfer it to the female.
I've tried the direct method of pulling of the male, removing the petals but found it faster & more efficient with the small paint brush.
I do the same for my pumpkins & zucchini squash in the garden (very few bees here to pollenate)
If the female cucs die off & turn brown, most likely they did not get pollenated,
(Same for zucs but they seem to rot starting at the tip where the bloom is attached)
I continually look for females blooming, & seem to have lots of males to get pollen from.
1st pic is a male, 2nd female with the bloom attached to the end of the little cuc.