Yeast starter question

I am thinking of moving to all grain soon and have a yeast starter question. Do you still add the same amount of yeast you would have used with out the starter after you add the yeast starter?

Also, when people reuse the yeast cake or slurry do they use a yeast starter then?

Umm, I'm slightly confused by your wording but here's what you do. You make your starter by boiling DME, let it cool, add the yeast pack, let it ferment out for a day, (optionally you can then cool it for a day and decant the liquid off the top leaving just yeast), then when your wort is ready you just pitch all that yeast.
Got it?

If you are reusing yeast slurry you should make a starter if it is old and you've been saving it in the fridge. If it is fresh, as in a few days, you should be ready to go.

In order to get a good, rapidly starting fermentation that will out compete the other microorganisms that might be in your wort you need to pitch a very large number of live yeast cells. Most yeast sold does not have nearly enough live yeast cells, particularly if you're producing a relatively high gravity beer. When you breed more of them, this is called a starter.

There are some calculators (e.g. mrmalty.com) that can tell you how much yeast is enough.

Typically a re-used yeast cake has plenty of live yeast if used immediately and does not need to be built up further.

Much depends on what beer you're making and how big it is. You can take a look at mrmalty.com to get an idea of how much yeast you use.
If I'm using dry yeast, I always rehydrate it. For big beers, I'll use 2.
For liquid yeasts, I always use a starter. I've not starting washing my yeast yet but yes, you most definitely should use a starter with them.

Really noob question, but thanks for the replies.

So the yeast starter will be all of the yeast you plan on using for the batch? And then depending on the gravity of the beer it should get up to a certain number before you pitch?

Mrmalty.com is very helpful.

Typically you will use 1 vial/smack pack with a 1 to 2 liter starter. Let that do its thing for at least 24 hours then pitch the whole thing. Some people put it in the fridge before pitching. This will make the yeast drop so you can decant some of the liquid.

If you are brewing a lager or big beer you will have to make a bigger starter.

How to make a yeast starter

More helpful info on yeast starters