The "High" voltage is Vdd-0.7V, the current available from any one port pin is 25mA. These are basic figures as used in most of the PIC controllers, and can be obtained by reading the datasheet, along with all sorts of other useful information.
The relay type has to be capable of a pull-in voltage slightly less than Vdd-0.7V and draw less than or equal to 25mA in order to be used directly from the port pin. Even though the port pins have protection diodes in them, I would still recommend that you put a protection diode across the relay coil to dissipate any back emf that is generated.
The arrow points to Vdd like this port pin o-->|--o Vdd
The relay coil being wired across or in parallel with the diode.
A better way to do it is with a cheap transistor and a couple of resistors, that way you don't need to worry about how much current the port pin has to offer, instead the transistor will be providing the "switching function"
Use say a BC337, put the emitter to Vss(Gnd) put a resistor around 10k from Vss to the base of the transistor, and another resistor around 4k7 from the base junction with the other resistor to the port pin. The relay gets wired between the collector and the Vdd, assuming it's a 5V relay of course. Also you still need the protection diode, but this time wire it between the collector of the transistor to Vdd, arrow still points to Vdd.
If you put two transistor output stages together, and drive two change over relays, you can arrange the wiring in such a way that you can not only start/stop the motor, but also change it's direction.