A splitter presents the same amount of attenuation between the in and all out ports. The level will be the same then on all outputs. One exception is the 3-way which will have one port 3.5db higher than the others. Consider that splitters are based on multiples of 2-way splitters with 3.5db attenuation per split. Attenuation values will be marked on the case near the ports.
Splitters are not symmetrical in that they will have a 3.5db attenuation between the in port and the out ports but from one output to another the attenuation will be very high. This is why you need to observe the input.
A tap will have an in and out port as well as one or more tap ports. The difference between a tap and a splitter is that a tap will take some amount of signal off a high level feeder line connected to the in and out ports and pass it to the tap ports. Taps are always connected in series on a line and are available in different values of attenuation (between the in and tap ports) to compensate for cable attenuation as you go along and the insertion loss of the taps before it.