There are various sites such as https://developers.google.com/speed/pagespeed/insights/ which will test the loading time of your page and give you suggestions for improving it. I would recommend you do that, and if you are unsure how to implement a specific recommendation, come back and post a new question about that issue.
Hi, we recommend GTmetrix which is a freemium ware to analyse your site to determine its speed. Go through each item in their analysis one by one to see what you can do to improve your sitespeed. It often comes down to having proper caching, image optimisation, script optimisation, having a CDN etc. While you could do all this, understand two things;
Site speed is ultimately heavily due to the web host. If you got a shared host, it is always going to be slower compared to dedicated or cloud host.
Dont be concerned too much about measurements with any tools. If your site is running fine and able to load from 3-5s, it is not that bad for viewing to be frank. The only concern here would be SEO for search engines which might rank your site lower. Unless you have a ecommerce or media site, actually it doesnt have to be found by search engines.