it is an SSRI and it does only act on serotonin receptors pre-synaptically, not heaps of receptors like the older TCAs and MAOIs did and as a result have a lot less side effects.
It's side effects are the same as any other SSRI - you could get dry mouth, nausea, diarrhoea, headache or nothing at all. But these side effects will only last a week or so and will disappear as your body gets used to it.
The reason to start on a low dose is to try and avoid getting the initial side-effects. Often if you titrate the dose up you don't get side-effects, or very minimal.
But you have to wait a few weeks before you see effects - they say 4-6 weeks on the correct dose, so that is 4-6 weeks after you have been taking the full dose he wants you to, but many people can see a difference in 2-3 weeks.
Congratulations on taking them.....it can be a big step.
Just my opinion but you should try them for the 6 weeks - if you notice no difference or you get bad side-effects you can always stop. You don't have to commit today to taking a pill forever, it's your body, only you know how it feels, but your doctor must think that it might help.