There are some simple rules in English for how to use present participle/past participle and relative pronouns with relative clauses.

First, relative clauses.

Type : Defining
Purpose : defines noun
Example
This is the shirt that I bought for €90, the rest were much cheaper.(that I bought for €90 identifies the shirt from many)

If the object of the verb in the clause (following the pronoun) is the same as the subject then the pronoun (and aux) can be taken out.
This is the shirt which is made for the typical tourist.

A non-defining relative clause is different.
Purpose: add extra info.
• between commas
• pronoun introduces clause
•• you cannot use that
Example
Many people in Spain, who live on the coast, were contacted for their opinion.

Without the extra info the sentence still makes sense (remember to take out the commas!).
Many people in Spain who live on the coast were contacted for their opinion.

Participle clauses
We are used to past participle in the passive.
The book was written by JK Rowling, and was very successful.

But we can simplify the passive.
The book was written by JK Rowling and was very successful.
But there has to be a clause after the participle.

Many cakes were being eaten. ✓
Many cakes being eaten. X
Many cakes being eaten at the party were horrible. ✓

Present participle clauses
An ing form without the verb to be is usually referred to as the present participle .
Swimming (present participle) is great fun.

We use it in active clauses, and a lot in relative clauses.
Look at this sentence with its pronouns.

The film which starred Brad pit and that was filmed in Japan was a wonderful experience.

Using past/present participle
The film, (comma) starring (present participle) Brad pit and filmed (past participle) in Japan was a wonderful experience.

We use participles to keep sentences simple and more fluid rhythmically.