When i see people in the gym that don't really know what to do - which is perfectly fine if you are new to fitness! don't be embarrassed! - I will always see people focusing on biceps heavily. What I don't see is them supplementing this exercise with triceps and while this is just a personal opinion, I think it is one of the most important muscle groups to include in your weight-training.
This problem seems to be more prevalent in women, and is sometimes referred to as "bat wings" or "bingo wings." If you have a bunch of fat on your arms, the only way to get rid of that is with caloric reduction or a calorie deficit, this is true of all other fat on the body as well. Don't get the wrong impression, the exercises that I am going to explain here are not going to turn the flab into muscle because this isn't biologically possible. Instead, just realize that I am simply referring to exercises that you should not ignore if you are already working out your biceps at the gym and would like to incorporate a triceps add-on to your routine.
pulldowns
This of course requires your gym to have some sort of cable pulldown machine and there are a wide array of ways to accomplish this. The trick is to keep your elbows in the same place (hence the mirrors all over most gyms) and then extend MORE than 90 degrees on your extensions. I see a lot of people that just do the bottom bit and this is because that part is easier.... it is also skipping the entire point of doing the exercise. If you want to engage the entire tricep, you have to extend beyond 90 degrees.
The side of the pulldown bar is irrelevant, so if your gym doesn't have a multi-purpose cable pulldown machine you can use the lat-pulldown bar but just make sure that you put our hands at the correct distance from center. Also, you might have to do the exercises slightly different since the weight stacks might not have been intended to to be extended that far.
The length of the bar is irrelevant. The positioning of your hands and how far you extend is the most important thing
If you find your elbows moving from a stationary position, reduce the weight. Stop trying to become Arnold on your first days. You are doing more harm than good if you don't follow proper form.
There are a lot of different attachments and there are benefits to each of them but in reality, these micro-focuses of the various grips only matter to people that are well beyond normie status and for us normies, we need not concern ourselves with such things.
Just focus on your elbows being in one place, completing a more than 90 degree angle and as with every exercise that you do keep your back straight. It is very easy to tweak your lower back doing almost any exercise in the gym and even if you don't notice it right away, there are plenty of long-term studies that have shown that improper form tends to always end up damaging the lower back.
As someone in his 40's that actually did do these exercises wrong for a while and has slight back problems now because of it, I can attest to the fact that these warnings to avoid engaging your lower back is a very important thing to remember.