Causal arguments claim that one thing causes another (e.g., smoking causes lung cancer). Validity means the conclusion must follow from the premises, but causal arguments aren't valid since they deal with probability (or likelihood), not certainty. So for those, you look at how strong or weak the evidence is for the cause-and-effect relationship.

Strong causal argument: Good evidence supporting the cause.

Weak causal argument: Insufficient evidence or counterexamples.

Hoping this helps!

Most of America's almonds are grown in California.

Most produce from California is exported to Brazil.

Therefore, some almonds are exported to Brazil.

The problem here is that the premises don't guarantee the conclusion—just because "most" almonds are grown in California and "most" produce from California is exported to Brazil doesn't mean some almonds specifically are exported to Brazil. They could be eating the almonds domestically in CA and sending other produce to Brazil.

To make it valid you could say:

All of America's almonds are grown in California.

Most produce from California is exported to Brazil.

Therefore, some almonds are exported to Brazil.

Premise 1 guarantees that all almonds are grown in California.

Premise 2 states that most produce from California is exported to Brazil.

With these two premises, it's guaranteed that some almonds (because "most" produce from California is exported to Brazil) must be exported to Brazil.

OR another valid option:

All almonds grown in California are exported to Brazil.

Most almonds in America are grown in California.

Therefore, some almonds are exported to Brazil.