By CE, Roger means "Common Emitter". This is the fairly common connection you see for a transistor where (for an NPN transistor) the emitter is grounded (often via a relatively small resistance), the input is to the base of the transistor (often via a resistor) and the load or a load resistor is placed between the collector and the positive supply rail.
Here is a very simple example:
In practice, unless the transistor is simply used to switch something on and off, some form of biasing is required. Biasing turns the transistor part way on. This means that an audio dignal input to the base of the transistor can turn the transistor on more (with positive half cycles) and off more (negative half cycles).
Without the biasing, only half of the waveform would be amplified. For audio signals this would produce huge amounts of distortion.
A very simple form of biasing is to attach a resistor between the base and some positive bias voltage.
The disadvantage of this circuit is that the output voltage is highly dependant on the transistor characteristics and the temperature. In addition any DC voltage on the input will affect the bias, and the DC voltage on the output will affect the bias of any following stage.
It is clear that there is no positive and negative output. The output MUST always be positive with respect to ground. The output is more properly described as AC with a DC bias, or perhaps DC with ripple
.
In practice, you might use a voltage divider to set the bias point as this makes the amplifier more stable. An emitter resistor provides negative feedback (which can be bypassed with a capacitor to provide higher gain at higher -- audio -- frequencies). Capacitors are used between stages to isolate the DC bias between each stage. It is the capacitor that allows you to have a truly AC (absent of DC bias) input or output.
So eventually you get a design that looks like this:
Not all single transistor amplifier stages look like this, there are many variations. In addition there are other ways to eliminate DC bias that do not require capacitors.
However, understanding a basic common emitter amplifier will help you in a huge number of cases where you need to use a transistor,
Oh, and you are right in questioning the statement about ohms law. In determining what value resistors to use there is more to it than just ohms law.
For more information, you might like to check
this out. Page 2 is where it starts talking about the common emitter amplifier.