Help with chocolate decorations......

Love to help, but first you need to learn how to temper chocolate.  Only tempering will give you the shiny glossy finish on chocolate.

If you don't know this technique, there is another way that doesn't require tempering.

Get a marble slab or a heavy floor tile, and put it in the freezer for at least 4 hrs.

Melt some chocoalte

Have a tube of some sort of the size you want, and clad this in wax paper or parchment paper.

Take out the marble slab, drizzle some chocoalte on it, and spread it out with a palette knife.  As soon as the chocoale starts to stiffen, remove it from the slab and wrap it around the paper clad tube.  Let this chill for at least an hour before sliding the chocolate tube from the paper. Pipe in your mousse.  You can also pipe your mousse into cylinders and freeze them, then wrap the chocoalte around.

This techniqe will not give you a glossy, shiny chocolate finish, it will be matte, but attractive.

Hope this helps

Acetate strips are available through most bakery supply stores. These can be cut into shapes like squares, cylinders circles, and what not. The tempered chocolate is painted on the strips and when cooled can be slipped off very easily.

what you also need are shapes to work the acetate into. for example, coat your acetate strip with chocolate then wind it into a genoise ring, or lay it over a rolling pin, etc...

tempering is straight forward, melt to 100-110ish (f) - they often say 120, but not really needed. drop the couverture (which has the necessary fat percentage+, or you may need to add oil) chocolate to below 80ish (f) and then bring it back up to temperature for working with, which is around 88 (f) for milk & white, or 90 (f) for bittersweet or semi. if you exceed those temps by more than a degree you will probably fail, so be gentle/careful on temperature (hence the double boilers). an ice bath at the ready really doesn't hurt either to help that process along.

cover something (eg your spatulae, or a strip of parchment) with the chocolate to test and if it doesn't set (start to harden) in less than a minute or two then you are probably out of temp and need to start over.

mousse on a tuile... piping bag ftw?

OP's from India, so those temps won't mean much.

To melt chocolate don't melt over 45 C

For dark cool down to 28 C by adding in more chips, then warm up to 32

For milk"                                                                                      " 31

For white"                                                                                     "30

Since the OP is in India,  a  caveat must be said about ambient temperature and humidity for working with chocolate ( I worked in S'pore for 5 years, like living inside a proof-box) . The ambient working temp should be around 20-22 C, any warmer and you'll have trouble with chocoalte setting up, if the ambient humidity is higher than 70%, forget it, you'll never get the chocolate to temper.

On the other hand, the "frozen marble method" was developed  specifically to adress the temp and humidty issues.

Hope this helps 

Oh, forgot something.

Double boilers for melting chocoalte come with a big caveat as well.  Make sure the water never boils, or never gets above 80 C .  If it does, steam will escape from around the sides of the bowl and collect and condense onto the melted chocolate. 

Any moisture + chocolate = cement/sludge and is unusble for chocolate work, but OK for baking. .

Microwaves work well for melting chocolate, and I've been doing this on a daily basis--in S/s bowls now for over 6 years --witht the same microwave.

Learning how to work with chocolate is sometimes best done right beside another person.