In phpMyAdmin, open the SQL query window, and you can use one of these basic commands.
Search

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SELECT * FROM tablename WHERE fieldname < 30

(30 is only an example value)
This will search (SELECT) *(all columns) from the table WHERE the interested field is a number less than 30.

If you only wanted to see certain field, you can run this instead:

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SELECT field1 FROM tablename WHERE field2 < 30

This is helpful if your database contains a lot of fields that are irrelevant to what you are currently searching for.

Insert
If you know the exact order of the fields, use this:

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INSERT INTO tablename VALUES ( "value1a", "value1b", "value1c", "value1d" ), ( "value2a", "value2b", "value2c", "value2d"  )

If not, use this code:

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INSERT INTO tablename (field1, field2, field3, field4) VALUES ( "value1a", "value1b", "value1c", "value1d" ), ( "value2a", "value2b", "value2c", "value2d"  )

Find & Replace (Update)

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UPDATE tablename SET field2 = "value2", field3 = "value3", field 4 = "value4" WHERE field1 = "user1"

The important part of this command is WHERE, which insures that the information is only updated for "user1" and not for other users in the database.
For example:

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UPDATE `DBname`.`tablename` SET `fieldname` = '1' WHERE `fieldname` = '0'

Another example:

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UPDATE `tablename` SET fieldname1 = replace(fieldname1,"findthis","replacewith") WHERE `fieldname2` REGEXP '0';

Delete
Removing specific data by searching a condition from a query window or command line:

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DELETE FROM tablename WHERE fieldname < 30

If the entire table is no longer needed, you can remove it by clicking on the "Drop" tab in phpMyAdmin or running this command:

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DROP TABLE tablename

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INSERT INTO `intodb`.`tablename`
SELECT *
FROM `fromdb`.`tablename` ;

Find (all entries with certain value) and copy to another table

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INSERT INTO `intodb`.`tablename1` SELECT * FROM `fromdb`.`tablename1` WHERE `fieldname` =value;

+-------+------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+------------+------+-----+---------+-------+
| a | int(11) | YES | | NULL | |
| c | datetime | YES | | NULL | |
| b | varchar(3) | YES | | NULL | |
+-------+------------+------+-----+---------+-------+

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ALTER TABLE tablename MODIFY b VARCHAR(3) AFTER c

The result:
+-------+------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+------------+------+-----+---------+-------+
| a | int(11) | YES | | NULL | |
| b | varchar(3) | YES | | NULL | |
| c | datetime | YES | | NULL | |
+-------+------------+------+-----+---------+-------+

Insert 3 columns/fields to the end of the table:

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ALTER TABLE `tablename` 
ADD fieldname1 datetime NOT NULL default '0000-00-00 00:00:00',
ADD fieldname2 varchar(20) NOT NULL default 'open',
ADD fieldname3 bigint(20) NOT NULL default '0'


Insert column/field 2 after column/field 1:

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ALTER TABLE `tablename`  ADD `fieldname2` BIGINT(20) UNSIGNED NOT NULL AFTER `fieldname1`

Insert columns/fields 2 and 3 after column/field 1:

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ALTER TABLE `tablename`  ADD `fieldname2` DATETIME NOT NULL AFTER `fieldname1`,  ADD `fieldname3` DATETIME NOT NULL AFTER `fieldname2`

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RENAME TABLE oldtablename TO newtablename

Alternatively, you can select the DB and click on the "Operations" link of the table. Under "Table Options", there should be "Rename table to." Enter the new name and click the "Go" button.