"Tourism" is the abstract noun,the name of that industry - for example "Most of our country's economy is based on tourism". "Tourist" is an adjective or a noun 'the tourist industry" a "tourist spot" "a popular tourist site". Or "he is a tourist from England" .The first examples show adjectives and the last one a noun.

'Tourism' is an uncountable noun referring to the industry, the business sector, or the phenomenon - 'turismo' in Spanish. 'Tourist' is a countable noun referring to a person who visits a location for pleasure - 'turista' in Spanish. The problem is that English doesn't have an adjective corresponding to the Spanish adjective 'turistico'. There isn't an equivalent for this adjective in English, so we put two nouns together to form a compound noun. For example, 'tourist activity' is an activity which tourists can do, and 'tourism product' is a product aimed at the tourism industry. If the noun you are describing refers to the industry as a whole. you would make a compound noun using 'tourism' e.g. the tourism sector. If the noun you are describing refers to the visitors themselves. you would make a compound noun using 'tourist' e.g. a tourist hotel.