lhs -> rhs or lhs rhs represents a rule that transforms lhs to rhs.
The character can be entered as -> or \[Rule].
lhs -> rhs evaluates rhs immediately. You can apply rules using Replace. The assignment lhs = rhs specifies that the rule lhs -> rhs should be used whenever it applies.
lhs rhs can be entered as lhs \[Rule] rhs or lhs -> rhs. In most cases, Rule is printed using .
Rule is a scoping construct (see Section A.3.8). Symbols that occur as pattern names in lhs are treated as local to the rule. This is true when the symbols appear on the right-hand side of /; conditions in lhs, and when the symbols appear anywhere in rhs, even inside other scoping constructs. See The Mathematica Book on the web: Section 2.4.1 and Section A.5.5. Implementation Notes: see Section A.9.3. See also: Replace, Set, RuleDelayed.
lhs -> rhs or lhs 
rhs represents a rule that transforms lhs to rhs. 
can be entered as 
->
rhs can be entered as lhs \[Rule] rhs or lhs 
. 