Orthodox Conversion to Judaism
Melachot and Muktze
Melachah (work) is prohibited on Shabbos.  The categories of forbidded work on Shabbos are sowing, plowing, baking, weaving, tanning hides, writing and building, kindling a fire and transferring from domain to domain.  (Talmud Shabbos 73a)
The Torah commands that "Six days work shall be done, but on the seventh day there shall be to you a holy day, a Sabbath of rest to G-d."  A single example of forbidden "work" is cited: "You shall not kindle a fire... on the Shabbath day."

The forbidden works are those actions that are mentioned in the Torah when it relates the construction of building the Mishkan and corresponding activities.
The Talmud enumerates 39 categories of melachot that are forbidded on Shabbos. 

For the full list of 39 Melachot, click here.

Here are some examples of 'modern' applications of the melachot: writing homework, typing on a computer, cooking eggs on a frying pan, driving a car, chewing gum while walking down the street, wearing a coat or shirt that has extra buttons on the inside that serve no function, carrying your keys in your pocket, buying something in a store, going to the movies, carrying your coat instead of wearing it, carrying your kippa instead of wearing it, carying a purse...

Muktze:

Muktze is a law which states that something which could not be used at the beginning of Shabbos, or which was put away in order not to be used, cannot be used the whole day.  Objects which have not been prepared - a raw potato, a stone on the ground, a fruit on a tree, are muktze and may not be removed.  On Shabbos, we are meant to live from within, from within the world we have built before Shabbos.
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