These are the main forms used. The forms in brackets are possible, but not as common.

• Notice that English likes to drop the relative pronoun when it defines the object of the clause.
• That is usually used as a subject after the following: superlatives, all, every(thing), some(thing), any(thing), nothing, and only: All that's needed is a little more time.
• We often omit that when it is the object.
• Prepositions can come either before relative pronouns or at the end of the relative clause.

These are the main forms used. The form in brackets is possible, but not as common.

• Note that there are no commas before and after defining relative clauses when written, and no pauses when spoken.
• Note that there are commas before and after non-defining relative clauses when written, and pauses before and after them when spoken.
• Prepositions can come at the end of non-defining relative clauses, but in a formal style they are usually put before the relative pronoun.

Which can be used in non-defining clauses to refer to the whole of the preceding clause.

Whose can be used in both defining and non-defining relative clauses to refer to possession.

What is used as a relative pronoun instead of 'the thing that' in some sentences.

• In defining relative clauses, when can be left out.
• Where cannot be left out unless we add a preposition.
• In non-defining relative clauses, when and where cannot be left out.

Why can be used to introduce defining relative clauses after the word reason. It can be left out.

• Present participles describe an action which is still happening: He dived into the sea to save the drowning child.
• Past participles describe the result of an action that has happened: She looked at the broken chair. The completed statue looked very lifelike.

When participles come after a noun, they are like reduced relative clauses.

• Participle clauses can describe actions that are going on simultaneously: She sat by the fire reading a book and sipping a mug of coffee.
• Participle clauses can describe actions that happen consecutively: Opening his suitcase, he took out a revolver.
• If it is important to show that the first action has finished before the second begins, the perfect participle is used: Having finished lunch, we set off.
• Participle clauses can express the idea of because: Being a mean person, he never spent more than he had to.
• Participle clauses can express the idea of result: It rained every day for two weeks, completely ruining our holiday.
• Participle clauses can express the idea of if: Taken regularly, aspirin can reduce the risk of a stroke.
• Participle clauses can be introduced by while, when, after, by, on, and since.

Many verbs can be followed by an -ing form.

Just has several meanings:

Just about means almost. It can express something that is nearly not possible.