There are two schools of thought on timings for starters, I like to split the difference. First option is fridge decant and pitch second is high krausen. I make a starter 3 days out from brew day (I actually culture from slants but the last step is the same if you are using a smack pack or vial). 24-36hrs sometimes up to 48hrs for the starter to finish fermenting you will see if go to high krausen or you will see evidence of it having been at high krausen or you might just see an accumulation of yeast that has flocculated out to the bottom of your stater vessel. When you see the yeast start flocculating go ahead and put it in the fridge. It will settle out form a pretty soild yeast cake in 24hrs. Here is when you choose, you can take it out a few hrs before you brew, decant the spent wort that is on top of the yeast and leave about 1" to 1/2" sitting on top of the yeast. You can then swirl this a pitch this slurry into the wort. Note it will take a good bit of agitation to get the yeast back into suspension don't be timid. The alternative is morning of brew day you can make another starter, you decant the original starter and pour cooled boiled wort on top of the first starter leave this 8-12hrs and then pitch everything into the fermenter. in theory you could try to time the first starter to be at high krausen when you pitch but I never seem to be able to make the yeast schedule and mine meet up so I make the starter store it then make the beer get the yeast going and pitch once you have done a few you will get a system nail down that works for you.
I choose option second option for no real reason other than I like the yeast to be ready to go I see less lag time that with the first version. I like this as it gives the microbes less chance at a foot hold in my beer, however you can start a real good argument saying one way is better than another on this forum.
When making your starter use anything that hold liquid and can be sanitizer the only reasons you want a flask is it is really easy to boil the wort in the flask on the stove (watch for boil overs and for gas stoves only) and you can cool it immediately in an ice bath (lab quality glass only) and the flat bottom on the flask is for a stir plate which dramatically increase your yeast cell propagation.
If I did not have a flask and a stir plate I would use the largest glass container your can find. You can boil it in a water bath on the stove with the wort inside. Typically your starter size will be around 1.5L (use a pitch rate calc as suggest mr malty) so a 3L container is good especially if you aren't using fermcap. Don't use an airlock either an a bit of aluminum foil or a piece of foam soaked in sanitizer this will allow O2 to get in so you make more healthy yeast.
Once you have boiled your starter cool very slowly if you have used an aluminum foil you can leave it sit on the bench for a few hrs and let it cool. Once it is cool enough to touch you can speed up the last bit of cooling with a ice bath/cold water. Flasks are made of special glass allowing them to be dunked in ice cold water while the wort is still boiling inside don't do this with anything but lab quality glass!
Now just like your wort, your starter want lots of O2 even more than you aerate your wort if you don't have a O2 set up shake the crap out of it and do this often. The more O2 you put in there the better. Yeast growth is only determined by Sugar+nutrients+O2 if you give them lots of that you will have fat happy healthy yeast. So once you have shaken it pitch the yeast which you smacked a few hrs before. Now just shake it as often as you can and watch the yeasties get ready to work for you.
I almost forgot yeast food don't make the wort any heavier than 1.040SG to much sugar makes it difficult for the yeast to survive due to the increase pressure the dense liquid puts on the cell walls and the amount of alcohol it will generate. The starter is like a training camp for running and marathon, the day before you run a marathon you don't go out and run 20 mile race so don't make your yeast do that. Add a pinch of yeast nutrient or some bakers yeast at time of boil (boil bakers yeast for 15min to ensure it is dead) the dead yeast makes good nutrient (just don;t tell the yeast they are eating their brothers).
I don't think I forgot anything sorry for the War and Peace description and this might seem complicated however liquid yeast is not as forgiving as dry yeast there is a lot more at play. Once you have done one or two your will get a system and you won't consider not doing a starter. The only time I have had stuck brews is with brews not using starters (first two I used liquid yeast and listened to the wrong people).