Its the last letter of each word, Tubby. So for your sentence it would be
U E S S N S
And then I make up a sentence with those letters
Usually Each Sad Spaniel Never Sings
Y H D L R S
Oh blimey thanks Pix - soz
here goes…
You have dimples like Rodriguez Salez
…and then you enter…
U E S E Z Z 
No probs, took me a couple of times to get it as well. So after your sentence, you put the last letters of your line after it (its just helpful for the next person who wants a go.)
U E S E Z Z
Usually early sunshine eats zapped zebras
Y Y E S D S
I like how you left out the sentence bit…Took me forever to come up with the Z’s but, got there eventually! haha!
Well done PK that was never gonna be EZ (easy) 
Your Young Erica Sewed Dads Socks
R G A D S S
Regarding general advice, don’t speak sarcastically
G L E T K Y
Good luck exercising today, keeping young.
D K G Y G G
Don’t Kids Get Your Gander Going
T S T R R G
The small tortoises require regular greens
E L S E R S
Emily loves smelling eager Rodger’s stew
Y S G R S W
Yesterday Sarah got Ron seriously wasted
Y H T N Y D
You Had Time Now You Die.
U D E W U E
Ugly dogs even woof under elephants
U S N F R S
Usually Sunday News Features Rough Saturdays
Y Y S S H S
Young yams succulent so have some
G S T O E E
Got Some Toffees Only Elephants Eat
T E S Y S T
The elephant swear yesterdays sweets triumph!
E T R S S H
Extra Terrestrials Rarely Seem So Harmful
A S Y M O L
A smart yoghurt mulls over life
A T T S R E