Hi so you are obviously here because you want to know how to use the summon command. Im going to show you how to make a skeleton holding a Flame I bow with an ice block for a head and wearing full diamond armour riding a skeleton horse name "Frost Bite", its a bit complicated so you can either just copy paste the following command or you can apply your patience and learn how to do it yourself, it's really not THAT hard and once you done you can impress your friends!!

Note if i put a letter in capital you have to also the same with gaps! Leaving out one capital letter will make the whole thing not work!!

So first im going to show you the command and then i am going to Explain what every part means/does.

/summon Skeleton ~ ~1 ~ {Equipment:[{id:261,tag:{ench:[{id:50,lvl:1}]}},{id:313},{id:312},{id:311},{id:79}],Riding:{id:"EntityHorse",Type:4,Tame:1},CustomName:"Frost Bite"}

Ok so the /summon Skeleton ~ ~1 ~ part means to spawn a skeleton 1 block above the command block, putting a ~ means where the command block is so when we did ~1 we made it one block above the command block.

Opening the curly bracket means we are kind of like describing the skeleton with various arguments (it does not matter how many or what order the arguments are), So i started with the Equipment argument.
So Equipment is like the heading of the list and just like in normal writing we then put the colon, we then put the square bracket because there are various items which we surround in curly brackets and in order to make the command block take all those items as one argument we use the square bracket.
We have 5 "slots" for the equipment every "slot" has curly brackets on both sides and the slot are in this order: Hand held item , boots , leggings , chestplate and then helmet. To put an item in those "slots" you must do id:(the items id).
If you want to enchant the item you have to type ,tag:{ench:[{id:(enchantments id),lvl:(what you want the level to be)}]} and you just have to continue this till you have all the armour you want.

So next we do ,Riding:{ so that we can tell the command block what the skeleton is riding and untill we close the curly bracket every argument we say has to do with what the skeleton is riding.
We then put id:"EntityHorse",Tame:1,Type:4 You can replace EntityHorse with any other entity and the skeleton will ride that entity, you have to put Tame:1 so that the skeleton can ride it and we then put Type:4 to show that it is horse species #4 which is skeleton horse.

And lost and pretty much least (Difficult) We than just do CustomName:"(the name you want)"

and walla! it might be frustrating but when you finally manage, understand and memorize the complicated way of the summon command you can feel like a programer and make amazing custom maps with no Mcedit!

If you have any questions, suggestions or problems feel free to Comment, if you want me to do another tutorial or just write a command to summon something cool that you can copy and paste Please tell me!! This has been my first ever blog and i hope it will be a start to many more blogs that will help! Thank you bye!