New entry term join (#7520)

* [Edit] SQL: SUBSTRING() (#7473)

* [Edit] SQL: SUBSTRING()

* updated an faq and some content tweaks to add keywords

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* Join term is added

* major content tweaks

* Update join.md

* Fixed the format issues.

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Author: Taahirahbz

content/pandas/concepts/dataframe/terms/join/join.md

@@ -0,0 +1,61 @@
+---
+Title: 'join()'
+Description: 'Combines columns from another DataFrame into the calling DataFrame based on the index or a key column.'
+Subjects:
+  - 'Code Foundations'
+  - 'Computer Science'
+Tags:
+  - 'DataFrame'
+  - 'Join'
+  - 'Pandas'
+  - 'Python'
+CatalogContent:
+  - 'learn-python-3'
+  - 'paths/computer-science'
+---
+
+In Pandas, **`DataFrame.join()`** combines columns from another DataFrame (or multiple DataFrames) into the calling DataFrame based on the index or a key column. It’s mainly used for merging DataFrames with different sets of columns but shared row indices.
+
+## Syntax
+
+```pseudo
+DataFrame.join(other, on=None, how='left', lsuffix='', rsuffix='', sort=False, validate=None)
+```
+
+**Parameters:**
+
+- `other`: Objects to join with the caller DataFrame.
+- `on`: Column(s) in the caller DataFrame to join on; must match the index in `other` if provided.
+- `how`: Type of join to perform — 'left', 'right', 'outer', or 'inner'.
+- `lsuffix`: Suffix to add to overlapping column names from the left DataFrame.
+- `rsuffix`: Suffix to add to overlapping column names from the right DataFrame.
+- `sort`: Sort the result DataFrame by the join keys if True.
+- `validate`: Checks if the join is of a specific type ('one_to_one', 'one_to_many', 'many_to_one', 'many_to_many').
+
+**Return value:**
+
+Returns a new DataFrame with columns of both joined DataFrames combined according to the join logic.
+
+## Example
+
+In this example, a list of words is joined into a single string separated by spaces:
+
+```py
+words = ['Codecademy', 'is', 'awesome']
+result = ' '.join(words)
+print(result)
+```
+
+This code produces the following output:
+
+```shell
+Codecademy is awesome
+```
+
+## Codebyte Example
+
+In this example, a list of characters is joined into a single string separated by commas:
+
+```codebyte/python
+print(','.join(['a', 'b', 'c']))
+```