Magic circle spell. Simple explanation?

[Where is my drink]

Im about to level an inquisitor to level 7 and i was looking at the spell "Magic Circle". Its kind of confusing, is there anyone who could cut the fat, so-to-speak?

On a side note-if that isnt a great spell i would like to know what would be better? or what would level 3 spell would be a good choice. it seems difficult to even find one i care about TOO much. i always hate having a spell that isnt really useful, so.

Thanks!

[Devin O' the Dale]

Magic Circle against X has 2 ways to cast the spell. 1 outward facing and 1 inward facing.

We will begin with outward facing:

1) summoned monsters of X alignment cannot enter the area (10'R) or contact (if awesome reach)
2) +2 AC vs X
3) +2 saves vs X
4) charmed, mental control gets a 2nd saving throw +2 to SUPRESS charm, mental control, etc if already effected and immune while spell is up form new effects

Now the inward facing: (2 versions (secure and unsecure)

Unsecure:

This version of the spell works in conjunction with the Planar Binding line and Dimensional Anchor.

Holds creature in place 1 day / level but can teleport and attack out.

Dimensional anchor stops teleport

Secure:
10 minutes dc 20 spellcraft
no spell resistance to escape
no attacks across
no teleport

That is most of it!!!!!! In general it a great spell against summoners, enchanters and planar creatures. Being able to supress some enchantments and ignore summoned monsters helps a great deal. The AC and Saves are good if the SR kicks in or you attack.

It is essential, read don't do it without ro be dragged off to hell, to the planar binding line. If you plan to use it to bind get dimensional anchor.

[Marius Castille]

Long-duration pro-evil that can help some of your allies if they're close. This protection overlaps with rings of protection and cloaks of resistance so I think it's only an okay choice. The other parts can be useful for summoning. I'd pick heroism before this.