Okay, you haven't gotten the best of advice so far IMHO. A picture would be great for IDing it, but if you bought it as a beginer and its got needles its probably a Juniper, do not mist it! Do not fertilize it! Connifers as a rule generally do not like to be misted (except ones like the monteray cypress and redwoods) and you fertilize only plants that are actively growing, not sick ones.
All Bonsai should be outside during the summer, fukien tea, Ficus and a few other broadleaved tropical trees are used and they must come inside during the fall and winter but these are not your trees.
the tree might be savable at this point, are all the needles browning? also is it still flexible? if its brown all over and brittle its too late, however if its still got some spring left in it it might not be too late.
Okay, chances are good that there are rocks ontop of your soil that have been glued on, you must take these rocks off, get out a hammer and chissle and smash these to bits, baring that maybe a screwdriver and a rock would work. These rocks do not aid in shipping good bonsai, its only the cheap and poorly done ones that they glue to rocks onto, masking there errors and depriving the roots of proper water and air. Once you have the tree free from the rocks check to see if it is root bound, pull it out of the pot, soil and all, if the roots are all in a tight little ball that looks like they pulled it out of another pot and just stuck it into a depression in the soil you will need to break this ball up, you need to look for root rot aswell, any root that is bloack and slimy has got to be cut back to a point were it is fresh, then you want to plant it back into some coarse loam (topsoil) gnerally speaking you want to take the topsoil thats small enought to run through 1/4th inch screen but not so small that it will fall through bugscreening. if you do not have these tools you can get a hold of some potting mix with vermiculite or perlits in it or take some topsoil and pick out all the big bits and put it on a bugscreen and shake it to get the fine particles out. If you have gone the topsoil rout I want you to add to that about 20% unp[ainted aquarium gravle or 30% pool filter sand, this is to improve drainage, take a small section of screen and put it over the drainage hole in the bottom of your pot and add the potting mix or homemade mix to the potand then add the tree, gently spreading out the roots, but do not put a layer of stones or coarse gravle in the bottom of the pot, this is done to improve drainage but it actually hinders it by encouraging the water to form a film were the layers transition. Now your plant is repotted, you have to focus on watering it right, Junipers are mountain plants, and dry mountains at that they like it when there roots dry out in between waterings, how you tell that this is happening most reliably is to get a cheap chopstick from a chinese resteraunt, one of the disposable unfinished wooden ones, and stick it into the soil right beside the base of the trunk, every day you pull it out and see if it is wet or dry, if it looks dry check it against your cheek if it is infact dry I want you to water the soil from above untill water runs out the holes in the bottom into the saucer you keep your plant on, then wait till all the water has run out and drain the saucer so that the bottom fo the pot is not sitting in water (if youve got it outside like you probably should you probably don't need a saucer) Now as for fertilizer generally when its looking better and growing again osmocote every 6 months is what Bonsaists use, although I tend to preffer the orgainic route, a soil drench of a fertiliser below 10-10-10 is an okay route but it takes frequent aplications and it is easy to accidentally burn out your tree.
Good luck, HTH
Edit: If you want to bring up the humidity without misting the tree a good way to do it is whats called a humidity tray, you get a large tray and pour water into it and have gravle in the bottom for surface area and then the water evaporates and the humidity helps the tree in the pot you have above it.
