I want to graph a 2d surface in 3d Euclidean space and then plot multiple trajectories along the surface. Is it okay to ask what free graphing/plotting tool might be suitable on the main site and how to go about it?
If the graphing task were closely connected to a specific mathematical problem, as opposed to a generic need to "plot multiple trajectories" on a surface, then your question might be suitable for the main Math.SE site. It is the nexus of using mathematical software for a specific (mathematical) problem that would make it on-topic there.
As the selection of Martin Sleziak's links to past Questions shows, there has been general discussion of the image creation process and tools here on Meta-Math.SE. In part this can be rationalized by referring to the Meta-Math.SE FAQ which mentions "how the software itself works" as suitable for community discussion here. While the software referred to is the system software that StackExchange provides, it is natural to concern ourselves with how best to create images that "work" within the StackExchange environment (including issues of hosting, formatting, editing, etc.).