There are many factors why your site is slow. Image size in KB (note physical size - example 300px by 400px) is very large. You have a video that is very long and taking time to load. Bad links to other websites that are making it hard for the search engine to find them (the 404 error think). So many other factors too.
But wordpress comes with a caching plug-in, make sure it is active. it is wp-cache.
Here is a website my Yoast that can give you more insight.