Hey there, I'm doing History too. Are you just doing straight history or a dual degree? If you're doing straight I'm in the same boat. Here is my understanding of the process.
You need to complete 120 credits worth of modules by the end of the year. 20 of these credits are used up by the module "Paths from Antiquity to Modernity" which you must take if you do history. You also have to choose another history module out of the others on offer, which will be worth another 20 credits. These are the compulsory requirements they stipulate you must adhere to. These two modules take up 40 credits, leaving you with 80 credits to fill.
Now, each of the 6 history modules are worth 20 credits, so if you take them all, you have your 120 allotment and that is fine. However, the department can allow you to choose from a list of other modules in different departments to make up the remaining 80. You might have an email today telling you these modules, I received one myself. The sort of modules you can choose from range from Archaeology to Languages to Philosophy.
Another point, the University advises you split your credits 60:60 in each semester. You have an Autumn semester and a Spring semester. The history modules on offer are split evenly with 3 in the Autumn and 3 in the Spring. This offers a lot of flexibility if you want to choose modules from outside the department. I am looking at taking 2 History and 1 Archaeology module in each semester, which will give me my full 120. Of course, you can experiment and see what you want to do.
Hopefully you will have received something through the post explaining some of this or an email. Either way, you need to choose your History modules by the end of Sunday I believe. You then choose your other modules (If you want to use credits in other modules) on the 21st and 22nd when you are at the University.
I hope the info above is useful. If anyone can add anything I've missed, that'd be great.