Of course it's not as simple as that! There are at least 3 ground symbols in common use.
https://www.rapidtables.com/electric/Ground_Symbols.htmlThe one we care most about is the COMMON ground - the triangle with the end pointing down. This is electrical COMMON whether it connects to EARTH ground by way of CHASSIS ground or not.
This is an arbitrary point and it is not always the (-) end of a battery. I could put a voltage divider around the outside of a 12V battery, ground the center point, call it common ground and the result is +6 and -6 volts relative to common ground. Think about a center tapped transformer. 6.3V either side of the center tap and 12.6V across the ends.
When you study circuit analysis, ground will usually be obvious and, for homework problems, is generally the lower left corner of the circuit. But it doesn't have to be! You can pick ANY point as 'ground'. Some choices will work better (easier) than others but they will all work.
When you get to op amps and look at single supply variants, you will see that arbitrary midpoint of the power supply created in every design (except for bizarre boundary designs). It is important to bias the op amp to mid range such that signals can vary above and below ground (AC signals). Again, this is where w2aew's op amp videos come in handy because he sometimes uses single supply op amps. For dual supply op amps, ground is at the midpoint between the supplies (usually).
Further in the op amp stuff, you will find out about a 'virtual ground'. An interesting situation where the op amp tries to create enough feedback on the (-) input to keep the difference between the inputs at 0V. If the (+) input is grounded (0V) then the (-) input is a virtual ground and also 0V. This is an IMPORTANT bit to understand. Kirchhoff's Current Law comes into play here.
The law is simple: The sum of the currents entering a node is exactly equal to the sum of the currents leaving the node. In short, current can't pile up nor can it spill on the floor. Or, what goes in comes out...
13 minutes into this video, you will see a voltage divider on the (+) input of an op amp. It is probably described much earlier. I just clicked an arbitrary time and the schematic showed what I wanted to talk about
That voltage divider puts the (+) input at half the supply voltage so the negative feedback will hold the (-) input at that same level.
Why don't you look at the Electrical Engineering path over at Khan Academy? I did the entire course in a day or so and it's quite good. True, it was all review but the explanations are pretty good. If you catch the math for capacitors and inductors, that's great. If not, there are other tutorials you can work through later. Don't worry too much about the math, most hobbyists don't need it to enjoy the hobby. But it is elegant!
What you WILL see is the range of applications of Ohm's Law and how it applies everywhere.