SELECT *;
  FROM ((a JOIN b ON a.f1 = b.f1) JOIN c ON b.f1 = c.f1)

Table a is joined with b -> result1
result1 is joined with c.

((a*b)*c)

SELECT *;
  FROM (a JOIN (b JOIN c ON b.f1 = c.f1) ON a.f1 = b.f1)
    
Table b is joined with c -> result1
a is joined with result1

(a*(b*c))

Use this rule:
on a SELECT command is the ON clause that fixed the evaluation order;
read the ON in left to right order and you can known the evaluation order.

For INNER JOIN associative rule is valid: ((a*b)*c)=(a*(b*c))