Hello Anushka!
You're most welcome. Sorry for replying so late to
your reply.

Great job with understanding what I wrote. You synthesized my thoughts, really well! Your ideas are correct as far as they go. See Section C, below for one clarification re: your #3.
After all that explaining, "this" and "that" are sometimes interchangeable. Sometimes we can use "is" or "was" interchangeably, too. This probably makes things more difficult. Sorry!
Section A: Simple way to think of "this" vs "that"
First, let's remember how we normally use "
this" and "
that" for nearby and faraway things. Then, we can think about times that are close to now, times that are far away. Here's my thinking:
"This" and "That" as the first word of a phrase...
"This" = close in time or space (present; nearby)
"This is the first time I have caught a fish."
(when the fish is on the hook or just after)
"This is a table."
(table is beside me, I'm pointing at it; I'm pointing at a picture of a table)
"That" = away in time or space (past or future – even if the distance is in the immediate past; or a spatial distance away; or pointing at something or emphasizing something)
"That's the first time I've ever caught a fish!"
(after the fish is in the boat; if exclamatory, use exclamation point; use contractions – that's and I've – when speaking casually or writing casual dialogue)
Section B. "This was" vs "That was" and "This is" and "That is"
However we don't use "This" with "the past perfect" as in my "tortoise example.
This was the first time I had caught a tortoise.
Actually, "This was" and "That was" both work fine with
past perfect when telling a story (narrative). Examples:
That was vs. This was +
past perfect (narrative)
"That was the first time I
had caught a tortoise."

(autobiographical narrative)
"This was the first time I
had caught a tortoise."

(autobiographical narrative)
I believe that it only comes down to style between these 2 sentences above.
"John remembered his birthday well because
that was when
he had made his first snowman"

(Use "had made" because he made the snowman before he remembered.)
"John stepped off the train.
This was (or
It was) the first time
he had been to Montreal. He was excited about going to the International Jazz Festival."

(fictional narrative)
...but if you are standing there, holding the tortoise in your hand, you would say,
"
This is the first time
I've caught a tortoise."

(during the catching of the fish, now)
"
That's the first time
I've ever caught a tortoise!"

(just after catching the fish, emphasizing with contractions and exclamation point – Usually, "That is" or "That's" points to something away from us or that we want to emphasize – note Jack's comment.)
Section C. Continuous Verb Tense: Present Perfect Continuous
1. For ongoing activities we use "This" with "the present perfect" as in my "tortoise example.
This is the first time I have caught a tortoise.
Yes. I would use your sentence above for
while I'm catching it (not still looking for it) or just afterwards.

"Ongoing" activities sometimes call for a
continuous verb tense (look for "ing"):
"I
have been catching a tortoise" – a strange thing to say while picking up the tortoise and placing it in the boat but grammatically, it works. This is a better context for the concept of an currently ongoing,
continuous tense:
"I
have been playing poker for an hour" (ongoing action, currently still happening)
"I
have been playing poker all my life." (recurring action makes is 'ongoing', in a sense; I still plan to play poker in the future) Notice the "ing" to signal that it's a
continuous tense.
...but with, "This is the first time [that]...", you'll want to use your #1 example here.
"
This is the first time I have caught a tortoise."
present perfect
Now, I really hope that I have not made things more difficult for you, or anyone!
Cheers,
Jaykay
