Here's my understanding about first and second conditionals.
If Tom has time, he will visit us.
It's an open narrative. If Tom has time, he will visit us. If he doesn't, then he won't.
If Tom had time, he would visit us.
It's unlikely Tom will have time, but there is still a slight chance he will visit us.
If Tom has time, he would visit us.
If Tom has time, his visiting is likely to happen. But he might decide to do something else. The speaker is just not sure.
He can catch the train, if you give him a ride.
The speaker is just narrating the truth.
He could catch the train, if you gave him a ride.
Not very likely the person can give him a ride. The person got something else to do.
He could catch the train, if you give him a ride.
If you give him a ride, it is possible he will catch the train, but not that likely.
Could anyone tell me if I understand the modal verbs and use them in conditionals correctly?
Because someone told me the verb and the modal should be in the same tense, like using "had" with "would" or "has" with "will".