Hi Mourisca
Your question relates to the use of articles.
To make a general statement using countable nouns you could use:
Zero article + plural noun: They go to the cinema on weekends
or
Article + singular noun: They go to the cinema on the weekend
Many sources will teach you to not include the article (as in example 1), maybe for simplicity purposes, but it is frequently used for academic purposes.
One academic source I use with my students says:
Am I making a general statement here? If yes, then look at the options for making general statements. If unsure, the safest strategy may be to use a plural noun with no article. (�)
There is a reference
here, rule 4 , that might help
Note: There is a SBE and SAE difference between on and at. In Australia we predominantly use "on" but "at" is understood.
Hope this helps
Cheers
Jayho