That sentence may have been difficult to follow as I'd written it, so let me rephrase it. Original sentence:
SeaGtGruff wrote:
Also, you can't visit Cyrodiil-- which is a war zone, so if you're just riding around sightseeing then you're at risk of getting attacked by other players-- until after your character reaches level 10.
Intended meaning:
"You can't visit Cyrodiil until after your character reaches level 10. Cyrodiil is a war zone, so if you're just riding around sightseeing then you're at risk of getting attacked by other players."
The portion before the opening long dash and the portion after the closing long dash were intended to go together as one remark, and the portion between the long dashes was an aside.
So in other words, Cyrodiil will be totally unavailable to you while your character is Level 1 through Level 9. When your character reaches Level 10, you'll get a system mail message inviting you to join the war effort, and you'll be able to queue for entry into Cyrodiil if you wish.
You cannot enter Cyrodiil by road or ship or wayshrine the way you can with other zones; the only way to get to Cyrodiil is to type L or select Alliance War in the menu bar, then queue for one of the various war campaigns. Depending on the size of the player population for your character's alliance in that campaign and your position within the queue, you might be able to get into Cyrodiil right away or you might need to wait for a bit before you can get in.
The same thing is true for the Imperial City; you must queue for one of the campaigns, and cannot queue for a campaign until after your character reaches Level 10.
While you're in Cyrodiil or the Imperial City, players from the other alliances can attack you. Each of the three alliances has an alliance base, which enemy players cannot enter under normal conditions, so you'll be safe from attack as long as you're inside your alliance's base. However, it's a little more complicated than that as far as Cyrodiil is concerned.
In Cyrodiil, each alliance has an alliance base which is split into two halves, and you cannot travel from one half to the other except by taking a transitus shrine. Each of these two halves is protected by a gate which enemy players cannot pass through as long as it's closed, so the large area behind that gate will usually be safe. There is a temple inside each of these two large areas, and each temple is intended to hold an Elder Scroll, so there are six Elder Scrolls in all-- two per alliance, with three alliances.
Part of the goal in the alliance war is to capture as many of the Elder Scrolls as possible. To capture a scoll from its temple, the enemy must manage to open the gate that protects the large area of the alliance base where the temple is located. If that gate is open, enemy players can enter that half of your alliance's base, try to capture its scroll, and try to escape with it, so if you're in that half you'll be a target since the enemy will assume that you want to stop them from capturing the scroll and escaping with it.
However, there is a smaller elevated area inside each half which the enemy cannot access, so if you're in that smaller area you will be safe even if the gate for that half of your alliance's base has been opened.
It all sounds rather complicated and confusing, but it's easier to understand once you've actually gone to Cyrodiil and seen it for yourself.
Cyrodiil itself is divided up into three extensive sections by walls and waterways, and each of these three sections is associated with one of the three alliances-- the alliance's home territory, so to speak. There are three gates in each of the dividing walls, and three bridges across the river, so to pass from one alliance's home territory to another you must go through one of those gates or cross one of those bridges. The gates and bridges can be destroyed to try to prevent the enemy from crossing into an alliance's home territory, but there is also an additional point of crossing which cannot be closed off.
Each alliance's home territory has keeps and outposts which contain transitus shrines, which are similar to standard wayshrines except you can't travel from a standard wayshrine to a transitus shrine, or vice versa, only from one transitus shrine to another. Furthermore, there is a network connecting the transitus shrines together, and you can only travel to a given transitus shrine if your alliance controls that keep or outpost and its connection is unbroken. Thus, you might be able to use a transitus shrine in your alliance's base to fast travel to a keep that's all the way on the opposite side of Cyrodiil, or you might be able to fast travel only partway across Cyrodiil, or you might not be able to fast travel to anywhere except to the other half of your alliance's base, depending on which keeps and outposts are controlled by which alliances.
Other than using the network of transitus shrines to fast travel across Cyrodiil, you can just walk or run or ride wherever you want to go. There are delves (essentially mini dungeons) all around Cyrodiil, as well as a few war-torn towns, so you can go questing if you wish, although you'll be questing in a war zone so you'll be fair game for any enemy players. That's how I normally spend most of my time in Cyrodiil-- doing daily repeatable quests for NPCs in the war-torn towns, and occasionally questing in delves, rather than fighting in the alliance war. But on occasion I like to join the fighting; I'm just not very good at PvP.