Wolfram Language & System 11.0 (2016)|Legacy Documentation
When you enter a piece of input such as 2+2, the Wolfram Language first recognizes the + as an operator and constructs the expression Plus[2,2], then uses the built‐in rules for Plus to evaluate the expression and get the result 4.
But not all operators recognized by the Wolfram Language are associated with functions that have built‐in meanings. The Wolfram Language also supports several hundred additional operators that can be used in constructing expressions, but for which no evaluation rules are initially defined.
You should realize that even though the functions CirclePlus and CircleTimes do not have built‐in evaluation rules, the operators and do have built‐in precedences. "Operator Input Forms" lists all the operators recognized by the Wolfram Language, in order of their precedence.