Yes they are very useful.
<input> is used to recognise what the user just said to the bot. So you could make a pattern like this:
<category>
<pattern>WHAT DID I SAY</pattern>
<template>You said "<input index="2"/>".</template>
</category>
The index indicates how far back in the conversation you want to go. So index=“1” means the current input. index=“2”, the 2nd to last and so on. In the category above, you wouldn’t want to use index=“1”, as it would go like this:
Human: Hi
Bot: Hi
Human: What did I say?
Bot: You said, “What did I say?”.
<that> is one of the tags used to keep context of the conversation and records what the bot has said so if the user answers something like “yes”, you at least have a clue what they are talking about.
<category>
<pattern>YES</pattern>
<that>DO YOU LIKE ME</that>
<template>Aw thanks. I like you too.</template>
</category>
<request> is the same as <input> but handles multiple sentences.
<response> is the same as <that> but again, handles multiple sentences.
Without trying to confuse you, if either you or the bot utters more than one sentence at a time, <input> and <that> will only store the last sentence and so you need to add an extra dimension to the index. Let us imagine the bot has just said:
Bot: Hi Karen. Hope you are enjoying AIML. Do you have a chatbot?
<that> would be “Do you have a chatbot”
If you wanted to refer to other parts of <that>, they are stored as:
<that index=“1,3”>Hi Karen
<that index=“1,2”>Hope you are enjoying AIML
<that index=“1,1”>Do you have a chatbot
(Notice how the index is stored in reverse)
where <response index=“1”> would be “Hi Karen. Hope you are enjoying AIML. Do you have a chatbot?”
I would concentrate on <input> and <that> while you are just learning AIML. The other tags are useful but you should learn the basic ones first.
I would STRONGLY advise learning AIML 1.0 before trying to master AIML 2.0. Not to do this would be like trying to learn advanced physics without first learning physics.
Hope that helps. Feel free to ask any further questions and I will be happy to help.