Some effects in the game could trigger only if you "place focus tokens on a card to…", other could trigger only if you "focus a card to…".
You can read about this important difference at page 10 of the official rules, in " A Matter of Focus", where they stated that
"Some card abilities or game rules require one or more focus tokens to be placed onto a card. This does not cause the card to focus (i.e. trigger an ability or take some other action) but it does cause the card to become exhausted."
By searching for the word "focus" in the rules, at page 16, "Generating Resources", they carefully avoid to use the wording "to focus" but they always use "place a number of focus token".
So until here it seems that you don't focus any card to generate resource, but instead you simply place focus tokens.
But at page 17, "Resource Example #1" they use another wording, only one time, but it is still enough for me to have a doubt.
On the third paragraph you read:
"He could generate one resource each from both “Cloud City Casino” cards. However, neither neutral resource would have the resource match required to play a Jedi affiliation card. Instead, he focuses one “Cloud City Casino” (generating one neutral resource) and the “Forgotten Heroes” objective card (generating one Jedi resource). With two resources, including one that matches the affiliation of “Trust Your Feelings,” the LS player is able to pay the cost of the card and play it."
So, the question is: if you want a card to generate resources, do you focus it - triggering effects like "when you focus a card.." - or not?