canon t3i... Alot to learn..

hi guys i bought my first DSLR.. i have used nikons in past and i am pretty use to their interface and buttons option. this is my first Canon T3i and i am still getting use to the usage

anyways i was playing around and took some pictures in manual mode but i seem to have tough time with exposure. like when i am in manual mode i can change the shutter speed and focal point but not the exposure.

in aperture priority i can change the exposure but not the shutter speed. so its kind of confusing.

also i will be using this camera for a small function next week and i am planning on buying a 50mm lens for it also for portrait photos and video recording.

now i tried using the video and i am having hard time focusing especially without the focus ring.

so is there any tips for new bee to take care of or keep in mind while making video?
i will be using a dolly and tripod stand for sure

thanks alot for all the replies in advance