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