TheEach float is nearly 5 meters tall and the parade was very interesting.

I'm going to introduce the summer festival in Sawara, Chiba prefecture.

"I'm going to tell you about..."
"I'd like to tell you about..."
"I want to tell you about..."

These sound more natural, but what you wrote is fine.

TheEach float is nearly 5 meters tall, and the parade wais very interesting.

I'm going to introduce the summer festival in Sawara, Chiba prefecture.

"I'd like to tell you guys about the summer..." sounds more natural.

The float is nearly 5 meters tall and the parade wais very interesting.

I'm going to am introduceing the summer festival in Sawara, Chiba prefecture.

This sounds better.

The summer festival takes place for three3 days in July.

Redundant use of summer. Usually, for numbers 10 or less, we use written numbers.

The most interesting part of the festival is the Yamaguruma parade.

There are 10 floats called Yamaguruma and each float has a big figure/statue on atop.

Prepositions and all that.

The float is nearly 5 meters tall and the parade wais very interesting.

Use consistent forms of "to be."

I want to show everyone the pictures.

I'm going to introduce the summer festival in Sawara, Chiba prefecture.

The float is nearly 5 meters tall and the parade wais very interesting.

OPTION A: The Sawara Summer Festival in Chiba Prefecture¶
OPTION B: Sawara's Summer Festival

NOTE: Many readers might not know about Sawara or have any idea where it is.

I'm going to introduce the summer festival in Sawara, Chiba prefecture - about 100 km east of Tokyo.

NOTE: For benefit of some people overseas, it might to indicate the location of Sawara. It is about 100 km from Tokyo, right?

Theis summer festival takes place for three days in July.

There are 10 floats called Y, known as yamaguruma, and each floatof there has a big figure/ or statue on top it.

TheMost float iss were nearly 5 meters tall and the parade was very interesting.

I want to show everyone the pictures.Listed below is a hyperlink with some pictures of this event:

I'm going to introduce want to tell you about the summer festival in Sawara, in the Chiba prefecture.

Yours is gramatically fine, but the correction is to make it more natural.

The summer festival takes place fover three days in July.

"over" is slightly more natural.

TheEach float is nearly 5 meters tall and the parade was very interesting.

This is fine, but the two ideas connected with "and" sound a bit abrupt and disconnected.

I want to show everyoneCheck out the pictures. here:

A more natural way.