The town where I live

I live in the Northwest of Spain, in a town south of Galicia. 

The town where I live is a industrial town called Vigo. It has a sea.(better to say: it is by the sea) Almost business fabric (I'm not sure what you mean here. Perhaps you are confusing the Spanish 'fabricia' for the English word 'factory'? I would suggest the sentence might be: 'almost all businesses are related to the sea') is related with the sea. The majority of factories process fish or seafood but there is a very important company that builds cars (A company that builds cars is also called 'a car manufacturing company) called PSA Citroen however there is also a very important company that perhaps you know. It is Inditex (Zara, Massimo Dutti etc) in this case (**I have made a similar correction already- for practise, try to correct thins one. I have put the right structure below) Galicia, in Coruña.

Vigo have nice beaches and good weather, nevertheless we are in fall, now we have very good temperatures because it is San Miguel's summer, it means that we have temperatures of 27 degrees centigrade. It only happens in this week of October. In the coming weeks  the rain will arrive and the temperatures will drop.

OK, there's a lot of yellow but that wasn't a bad attempt. They were mostly small mistakes, so this is good! :)

**It is north of Galicia, in Coruna.

The town where I live

I live in the Northwest of Spain, in a town of Galicia's South. (In the region of Galicia's South)

The town where I live is a industrial town called Vigo, it has sea (It is located by the sea). Almost business fabric is related with the sea, (Almost all products manufactured by the businesses are sea-based) the majority factories are of processed fish or seafood but there is a very important company of building cars called PSA (You can also simply say, majority of factories in the city deal with fish processing and seafood) Citroen however there is too (also) a very important company that perhaps you know it is Inditex (Zara, Massimo Dutti etc) in this case it is in the Galicia's North, in Coruña.

(The better sentence in my opinion would be, "Not only Galacia is famous for the car manufacturing company Citroen, it also hosts brands like Inditex (Zara, Massimo Dutti, etc) and they're located in the North in Coruña")  

Vigo have nice beaches and good weather, nevertheless we are in fall, now we are having very good temperatures (you can also say, "now we're experiencing/enjoying good temperatures") because it is San Miguel's summer, it means that we have temperatures of 27 degrees centigrates, (celsius) it only happens in this week of Octuber. (October) It will be sure the next weeks will arrive the rain and the temperatures will drop. You can say (It will last for a few weeks before the rains arrive making the temperatures drop.) or (It will last until a few weeks before the rains arrive and the temperatures drop). 

The town where I live.

I live in the Northwest of Spain, in a town called Galicia's South.

The town where I live is a industrial town called Vigo, it has a coast. Almost all business is related with the sea, the majority of factories are of processed fish or seafood. But there is a very important company that makes cars called PSA Citroen however there is also another large company that you might have heard of, it is called Inditex (Zara, Massimo Dutti etc) and in this case it is in the Galicia's North, in Coruña.

Vigo has nice beaches and good weather, however while it is now autumn, we are having very good temperatures at the moent because it is San Miguel's summer, it means that we have temperatures of 27 degrees centigrates, it only happens in this week of October. I'm sure in the coming weeks the rain will arrive and the temperatures will drop.