Sacramentals are items used in the Church that are channels of grace with spiritual power.

Examples of these objects are:

Holy Water
Holy Salt
Holy Oil
Scapulars
Rosaries
Chaplets
Statues
Holy Images
Icons
Crucifixes
Liturgical/Blessed Candles
Medals
Blessed Palms (From Palm Sunday)

These are items used by the faithful for various reasons and Purposes

Holy Water, Oils & Salts are used to bless oneself, home, or even to ingest. Crucifixes, Holy images, Icons are meant to assist us in focusing our attention on the divine away from the world. To use the senses we use to focus on the world to instead be not tricked, but absorbed by the divine so that the world isn't penetrating that focus and lifting up of one's soul.

Rosaries, Chaplets, Devotionals are to assist one in their prayers through a set series of prayers and meditations as human beings are attracted and need an ordering. One doesn't need A ROSARY to pray the rosary but they do help to keep track and stay focused and undistracted.

Use:
Any Holy Item needs to be blessed before it becomes that channel of grace. Water that isn't blessed is just water and a candle burning on your home altar is just a candle from Walmart without being blessed.

It can be hard at times to find priests willing or sadly, knowing that there are specific prayers for specific items. For instance, the St Benedict prayer for items containing the medal has a specific exorcism prayer along with the general blessing of a religious item. I have found the more traditional the priest/parish the more aware they are of this and are happy to do this. Holy Water for instance is SUPPOSED to have blessed salt mixed in with it, while some priests are unaware these days and just bless the water. Does this make it "unblessed" or regular water? No, but as Father Ripperger of the Doloran Fathers has said on this subject "You get out what you put in". In his experience, if the St Benedict medal has just a regular blessing it has less usefulness than one that has in exorcisms, and we are in an eternal battle and should be getting the most "high end" equipment for our battles as we can.

Sacramentals are a very powerful tool that has sadly become shelved in the last 60 years. Luckily my mother-in-law for years was sending us holy water, holy oils, holy salt that helped keep this tradition in front of me until my rediscovery of these traditions myself in the last few years. I now annually re-mark around the house and property with Holy Salt and will be doing a ceremony (once the chapel is finished) of burying St Benedict medals and having the property exorcised/blessed.

Note of Importance:

Sacramentals should not be viewed in the irreverent Hollywood fashion as being some sort of magic talisman (i.e. throw holy water on a vampire) that it, the object, is what has the power to assist you in the fight against evil, but it is the power of Christ of the One Living God who is the source. He has given the Church these sacramentals as channels of his grace, physical items for spiritual protection so that we may recognize even more our need for his grace in our lives.

Disposal:

We all have, or you will have, Rosaries at home that have broken and aren't able to be repaired easily and need to be gotten rid of. The proper way to dispose of a blessed item is these...

Icons/Holy Pictures/Scapulars/Combustible items:
They are to be reverently burned and then the ashes buried in a place that won't be walked on, say the woods or wherever is less touched by the feet of man.

Rosaries, Chaplets, etc:
They are to be broken apart into pieces so that they don't look like what they were. A rosary in half looks like half a rosary, each bead removed becomes a pile of beads and chain and then can be thrown away or buried. An item loses its blessing once it no longer looks like what was originally blessed. I usually take the crucifixes off and bury them under the house or along the property line.

You should also note that the church teaches that selling of sacramentals removes the blessing from the item. They are meant to aid the faithful not be used as a business. With relics of saints its actually a sin to sell them. To buy them is permitted but to sell is not, they should be once in your possession be donated to a church or individual.