Introduction:
In this article,explained the c# Contextual Keywords with simple definition for better understanding.

Main:

from Used in a LINQ query. A query expression must begin with a from clause.

get Defines an accessor method in a property or indexer. It retrieves the value of
the property or indexer element.

group Used in a LINQ query and returns a sequence of IGrouping < (Of < (TKey,
TElement > ) > ) objects that contain zero or more items that match the key
value for the group.
into Used in a LINQ query and can be used to create a temporary identifier to store
the results of a group , join , or select clause into a new identifier.

join Used in a LINQ query for associating elements from different sources.

let Used in a LINQ query to store the result of a subexpression to be used in a
subsequent clause.

orderby Used in a LINQ query to sort the result of a query in either ascending or
descending order.

partial Denotes that the definition of a class, struct, or interface is split into multiple
files. Also denotes that a method ’ s signature is defined in one partial type and
its definition is defined in another partial type.

select Used in a LINQ query to specify the type of values that will be produced
when the query is executed.

set Defines an accessor method in a property or indexer. It assigns a value to the
property or indexer element.

value An implicit parameter in a set accessor. It is also used to add or remove event
handlers.

where Used in a LINQ query to specify which elements from the data source will be
returned in the query expression.

yield Used in an iterator block to provide a value to the enumerator object or to
signal the end of iteration.

Conclusion:
Hope this helps,
Happy Coding.