In this Blog i'm going to explain each command thoroughly.
So lets begin.

To get a Command Block you need to enter the command:/give @p 137
To get a Command Block Minecart enter the command:/give @p 422

1.TP - Usage:/tp [name of player] [x] [y] [z]
~use this command to teleport a player to a certain location.
You can Also use this symbol ~ to teleport a player to how many blocks the x y z coordinates point to.

2.give - Usage:/give [player] [item id] [quantity] [damage value] [data tag]
~this command is used to give items to players.
example:/give @p 54
This means it will give the nearest player a chest.
you can also use:
/give @p minecraft:chest or
/give @p chest
How to use the data tag to give items.
Now, the data tag feature was added to 1.7.2 it uses nbt tags so that players can actually give custom items
without using so many command blocks.
How to use this feature:
example:/give @p wood_sword 1 0 tag:{ench:[{id:34,lvl:10}]}
In this example this command is giving you a wooden sword that has the enchantment Unbreaking with the level of 10 on it.
There are also other ways to use this for example using this command you can give a player an item with a custom name.
/give @p iron_sword 1 0 tag:{display:{Name:Long Blade}}
There are tons of other ways to use this feature, but i'll go over it next time.

3.say - Usage:/say [message]
~This command will put in the chat box the message that has been inputed.

4.tell - Usage:/tell [player name] [message]
~Just like the say command except it doesn't show it to other players except the designated player.

5.scoreboard - Usage:/scoreboard [objectives,teams,players]
~This is quite complicated unless you understand how to use this command.
objectives - Use this to add, remove, setdisplay and list objectives for your world
How to use:
/scoreboard objectives add [name] [criteria] [display name]
/scoreboard objectives remove [objective's name]
/scoreboard objectives setdisplay [display area] [objective's name]
/scoreboard objectives list
/scoreboard teams add [name] [display name]
/scoreboard teams remove [team's name]
/scoreboard teams join [team's name] [player]
/scoreboard teams leave
/scoreboard teams option [team's name] [color,seeFriendlyInvisibles,friendlyfire]
/scoreboard players set [player's name] [objective's name] [amount]
/scoreboard players add [player's name] [objective's name] [amount]
/scoreboard players remove [player's name] [objective's name] [amount]

6.enchant - Usage:/enchant [player] [id] [level]
~This is to enchant the item you are holding it can only be enchanted unless the enchant is for the item itself,but there is an
exception to this rule do to the new data tag feature.
The maximum enchant you can do with this command is how high it can be in the enchantment table.
But once again an exception with the data tag feature has occured with this it can now be up to 999999.
The command:/enchant @p 0 1
Data Tag:/give @p iron_sword 1 0 tag:{ench:[{id:16,lvl:999999}]}

7.effect - Usage:/effect [player] [effect id] [Amplifier]
~This comand allows you to effect players wit certain effects
ex./effect @p 1 10 5
1 is where the effect is
10 is how long it lasts
5 id how strong the effect is

8.summon - Usage:/summon [EntityName] [x] [y] [z] [DataTag]
~Used to summon Mobs and other entities that are customizable.
ex./summon EntityHorse ~ ~1 ~
ex2./summon EntityHorse ~ ~1 ~ {Type:3,Tame:1}
example 1 summon a Random Horse as while example 2 summons A Skeletal Horse that is tamed.

9.setblock - Usage:/setblock [x] [y] [z] [block id] [Data Tag]
~This is used to set a block within the world.
This works for all blocks including mob_spawners
ex./setblock 100 100 100 minecraft:dirt
You can also use data tags with this command.
ex./setblock 50 20 90 minecraft:chest 0 replace {TileEntityData:{Items:[{id:1,Slot:5,count:1}]}}
If there is no count then the item will be a phantom item which wahtever you do with that item it will immediately disappear.

10.tellraw - Usage:/tellraw [text]
~I have not personally used this command myself so I put the video showing you at the bottom of this post
The video is not nor do I own it it is simply a video tutorial that I inserted here.

11.setworldspawn - Usage:/setworldspawn
~Sets the worlds spawn chunks to where the command was previously used.

12.gamemode - Usage:/gamemode [mode] [player]
~This is used to change the gammeode of players the modes are 0,1,2

13.gamerule - Usage:/gamerule [rule] [value]
~Used to change certain rule of the game.

14.weather - Usage:/weather [clear,rain,thunder] [time]
~This is used for certain weather types

15.toggledownfall - Usage:/toggledownfall
~this toggle the rain.

16.testfor - Usage:/testfor [player]
~this is used to test for certain players or the amount of players within a certain area.

17.testforblock - Usage:/testforblock [block id] [x] [y] [z]
~used testfor certain blocks in certain areas of the world

Ok this is the end of this blog post if I missed anything just tell me.