[Damo]

If you're new to the game, I'd suggest using the default interface until you get used to it. OLC GUI is mainly aimed at those using manual targeting (a science in itself) and those marks on the periscope are there to aid you in this, like Angle on Bow etc. You could always take a look in the SH3 Mod workshop or downloads section and download OLC GUI simply to have a read of the user guide which will make things (somewhat) clearer. There are other GUI's aswell, it's a question of personal preference. I use MAGUI which is based off of OLC with many tweaks and enhancements but probably better to take things one step at a time as a new GUI will steepen the learning curve considerably.

The forums here are a wealth of knowledge, with pretty much every problem, niggle, addon, mod, and game feature discussed extensively, so use the search function and your queries will be answered.