Question

how did you understand the slogan no taxation with out representationl

Answer 1

the american colonies therefore raised the slogan NO TAXATION WITHOUT REPRESENTATION in 1774 representatives from all colonies except georgia met in protest at a congress at philadelphia

Answer 2

It was a rule in British Parliament that "Taxation without representation" so the slogan was raised before American Revolution by North American Colonies before their British Rulers to have their representation in the British Parliament. So American raised the slogan "No taxation without representation" to have legislators seats in London.
James Otis was the person who raised this issue in 1765 in the Stamp Act Congress and a small number of people supported him.