Equalization is one of the most important effects placed on vocals, especially during mix down. Mixing down is one of the final processes when the individual tracks are combined into one stereo track. Most mix engineers will first listen to the vocal tracks and raise or lower their levels accordingly. Once the tracks have been soloed, the engineer will also apply any necessary equalization, which most typically involves a boost of 3 db at 3 kHz. This adds clarity to the vocals and can help them be heard above the instruments without sounding unnatural.
Compression is added after the equalization is set. Compression squashes the signal by varying amounts to help sounds be heard over others or in conjunction with others. Vocals are often dynamic and can be hard to hear over instruments, but adding compression can help the softer passages be heard clearly as well as tame loud syllables. Most mix engineers add 2:1 compression to start and move up as needed. The ratio dictates how much the output is reduced above a set threshold. Higher ratios often result in a "squashed" sound.
Reverb is one effect that is almost always added to vocals during the mixing process, unless the vocals are recorded in a non-dead room. The effect allows the vocals to breathe and sound natural, as if the vocalist were singing in an arena or small club. You can set the reverb type as well as the amount, and many reverb software programs use room types to dictate the qualities of the reverb itself. "Small arena" and "live room" are much more than catchy names; they simulate the sound in those types of venues.
Delay is used on vocals but must be used judiciously. Sound naturally travels, hits walls and other obstacles and echos. Delay is an effect that simulates this action and can be useful on vocals if used sparingly. Delay is great for the end of vocal lines, when the lyrical content is important and the mix engineer or artist wants the word or phrase to carry on into the next bar of music. You can set the number of repeats, the strength of each repeat and the delay time based on the rhythm of the vocal line.