There are three main things you will be controlling when you are using your camera in manual mode: aperture, shutter speed, and ISO.
Apertures have different number ranges with each lens you use. The smaller the number, the more "wide open" your lens will be, and the shorter your depth of field is, Wide open apertures also allow MORE LIGHT to enter your camera which is great when you are using natural light indoors.
Wide open apertures also produce more bokeh (background blur). This is something that is much saught-after and makes your subjects pop and stand out. The opposite effects happen when your aperture is more "closed" (aka a higher number).
And for all my visual learners out there, here is an image showing how aperture works:
My favorite lens is my Sigma Art 35mm which has an aperture range from f/1.4 to f/16. I love to shoot wide open so if I am just taking pictures of my son, I keep it between f/1.4 to f/2. What aperture you use also depends on how close you are to your subject(s), and how much of the image you want in focus.. I could go on and on but just want to introduce the basics (these are supposed to be EASY tips, right?!)
And next, I will tell you what I know about shutter speed..
Faster shutter speed = less light enters your camera; better at stopping motion
Slower shutter speed = more light enters your camera; not as good at stopping motion
For low light situations, you should use a slower shutter speed. For situations with a lot of light, you can speed up the shutter speed until your image is properly exposed. In low-light situations, I like to keep my shutter speed to at least 1/250 of a second. This seems to give the best "stopping of motion" with my energetic toddler. If you take your shutter speed below 1/100s, you may want to consider using a tripod to avoid any hand shake blur (unless blur is your jam).
In brighter situations, I have had to increase my shutter speed to the max (1/4000s) and also clos down my aperture to get the right exposure for my images.
ISO determines your camera's sensitivity to light. Increasing my ISO is something I do in low-light situations when I have my aperture where I want it and my shutter speed slowed down but still need more exposure or light for the photo. ISO capabilities vary from camera to camera. With my Nikon D750, I can crank up my ISO pretty high (3,000-10,000 if needed). I shoot indoors pretty frequently so ISO is something I use on almost a daily basis. A lot of people will warn you not to crank it up too high because it will cause a grain texture in your photos, but I LOVE the grain. My camera usually doesn't show grain until I increase the ISO to about 5,000 but I don't mind when it does. The grain adds an extra element to the photo and I love photos with texture. Sometimes, I even add grain on purpose when I'm editing. My point: DON'T FEAR THE GRAIN.
I cannot teach in one blog post how to shoot in manual mode, HOWEVER, I can tell you that reading this guide book (below), plus countless YouTube video tutorials on shooting in manual mode really helped me! Searching for a tutorial for your specific camera is also very helpful since some control wheels and buttons can vary from camera to camera.
The book I mentioned on amazon: Tony Northrup's DSLR Book: How to Create Stunning Digital Photography
Lastly, if manual mode is WAY too scary for you at first like it was for me, try shooting in Aperture mode ('A' on most cameras). This mode allows you to control just your aperture while your camera adjusts for the shutter speed and ISO. This mode can help to be a stepping stone to full manual mode, but don't stay in this mode forever! Learning manual mode will PROPEL your photo-taking abilities.