Althoughthere is already a good solution provided by @ManishSolanki (and I would go for it), I want to show another easy way:
slice(
'https://webaddress.com/extracttion/',
add(nthINdexOf('https://webaddress.com/extracttion/', '/', -2), 1),
nthINdexOf('https://webaddress.com/extracttion/', '/', -1)
)
You can find the last positions in a string by using negative numbers as occurrence in nthIndexOf().
nthIndexOf('<text>', '<searchText>', <occurrence>)