What a yoga is
A yoga is a specific combination of planets that classical texts single out by name and attach a result to. Some are formed by a conjunction, some by an aspect, some by one planet ruling a particular house and sitting in another. There are hundreds, and a typical chart forms a dozen or more.
Strength decides everything
The presence of a yoga is only the beginning. A yoga formed by weak, combust or badly placed planets delivers very little, while the same combination formed by strong ones can define a life. This is why a list of yoga names, without the strength of each, tells you much less than it appears to.
When it acts
A yoga generally expresses during the periods of the planets that form it. A powerful combination whose dasha never runs prominently can pass almost unnoticed, which is why yogas are read alongside the Vimshottari dasha rather than on their own.
Common questions
How many yogas does a normal chart have?
A dozen or more is entirely ordinary. What separates charts is not the count but how strong the yogas are and whether their planetary periods run during a lifetime.
Is Raj Yoga rare?
Raj Yoga is a family of combinations rather than a single one, and some form of it is common. The forceful versions, formed by strong and well-placed planets, are much rarer than the name suggests.
Does a malefic yoga mean something bad will happen?
Not by itself. Many are cancelled by other factors in the chart, and a weak one often produces little. The cancellation rules matter as much as the formation.