Introduction of crossword puzzles

What is a Crossword puzzle?

A crossword is a word puzzle that normally takes the form of a square grid of black and white squares.
The goal is to fill the white squares with letters, forming words or phrases, by solving clues which lead to the answers. The answer words and phrases are placed in the grid from left to right and from top to bottom (In languages which are written left-to-right).
The black squares are used to separate the words or phrases and cannot be filled with letters.

Squares in which answers begin are numbered. The clues are then referred to by these numbers and a direction, for example, "12-Across" or "6-Down".
Numbered cells are labeled consecutively, usually from left to right across each row, starting with the top row and proceeding downward, Numbers are never repeated

Typically, clues appear outside the grid, divided into an Across list and a Down list.
The first cell of each entry contains a number referenced by the clue lists.
For example, the answer to a clue labeled "25-Down" is entered with the first letter in the cell numbered "25",
proceeding down from there.

Answers are in upper case letters. This ensures a proper name can have its initial capital letter checked with a non-capitalizable letter in the intersecting clue.
Diacritical markings in foreign loanwords are also ignored for similar reasons.

Clues

In straight crosswords (the ones on this site), the clues are simple definitions for the answers.
Often, a straight clue is not in itself sufficient to distinguish between several possible answers (often synonyms),
and the solver must make use of checks to establish the correct answer with certainty.
The crossword clues and their answers always has the same tense and number. If a clue is in the past tense, then so is the answer

Types of clues

1. Fill-in-the-blank clues are often the easiest in a puzzle, for example, "—— Johnson, explorer" = Osa
2. Abbreviations, A crossword creator might choose to clue the answer SEN (as in the abbreviation for "Senator") as "Washington bigwig: Abbr." or "Member of Cong.", with the abbreviation in the clue indicating that the answer is to be similarly abbreviated.
3. Variant spellings, The use of "Var." indicates the answer is a variant spelling (e.g., EMEER instead of EMIR).
4. The use of foreign language or a foreign place name within the clue indicates that the answer is also in a foreign language. For example, ete (French for "summer") might be clued as "Summer, in the Sorbonne" while Roma could be clued as "Italia's capital."
5. A question mark at the end of clue usually signals that the clue/answer combination involves some sort of pun, e.g., "Grateful?" = ashes (since a grate might be full of them).
6. The clue "Compass point", for a three-letter answer could be NNW (for north-northwest), ESE (for east-southeast), etc., but until a check is filled in, giving at least one of the letters, the correct answer cannot be determined.
7. Sometimes clues can contain "speech"-like answers, for example, entries in the puzzle grid that try to replicate our everyday colloquial language. In such a puzzle, one might see phrases such as AS IF or WHADDYA WANT.