How do we stop coming ads in our mobile screen?

Most apps which are free thrive on ads for their revenue. However they also will be having the paid versions which will not be showing ads.

The general and easy way to prevent ads being displayed is by using adblocking software, There are various ad blocking software available for free also. But even they may not be effective in certain cases.

So you can try them and find which one solves your problem.
There are ad blockers for browsers and /or apps. You may verify the suitable one and keep the suitable level settings.
You may verify the apps installed in your mobile and disable or uninstall any suspicious app. Then check if the problem is solved.
You may also use a mobile security programme which also may have an inbuilt malware/adware blocker. Regular scanning of your device by the security program will be useful. You may keep your browsers, security programme and used apps kept update.
Fro my experience I can say that Opera Mini browser blocks much advertisements.

Yes. You are correct. Some app developers see that on the screen of the user's phone some ads will pop up through their ads. The app developers have to earn money. So they see the users of their free versions of apps will get some apps on the screen of their phone so that the developers will get some money. There will be paid versions of these apps which are advertisements free. If we purchase those apps, we may not have this problem. The best way is to remove all unnecessary apps from our phones. But we can use the free versions and we can avoid these ads on our mobiles. It can be done through the Google Chrome app following the sequence mentioned below.
1, Open the google chrome app on your phone.
2, Then tap on the 3 dots icon.
3, A list will drop down and select settings from that list.
4. Then select the site setting from the list.
5. A list will appear on the screen. Click on the item" pop-ups and redirects".
6. Put off this setting
7. Then select ads from the list and put off the same.

This should ensure that the pop-up advertisements will stop. If still, the problem persists, there may be some virus on your phone. It is better to contact the customer care centre of your phone supplier.

Some of the best Ad blockers for Android and iOS are as below;

AdAway for Android
Adblocker Plus for Android
1Blocker X for iOS (iPhone)

I suggest you to go to Google Playstore (Android) and type ad blocker. The best one will come on the top and check the download counts and its review before downloading and using it. Likewise for iPhone users (from App Store) - check the review and download it.

These will help mostly to block the adv while searching or browsing. Firefox and its setting would also help you to block the ad (from Adblocker download and setting). Opera Mini also would help you for sure.

Websites earn revenue generated by the ad banner impressions and clicks but despite this sometimes the ads appearing on the platform might be quite annoying and sometimes even malicious. Its behaviours become unpredictable very often starting video plays or audio clips while in others ads are pouring continuously on pop - ups pages.
However, there are several ways of arresting them with the initiatives of taking up setting changes in the web browser.
We might apply Chrome to block ads on the websites if the same is accompanied by play sounds. We need to apply the following activities in the chronological stages-
1) Opening up the chrome browser
2) Tapping the 3 dot menu appearing in the right corner
3) Let the settings be tapped.
4) Site settings are to be scrolled down and tap on it.
5) Go in for pop ups and redirects.
6) Ensure that toggle is turned on.
7) We need to go back to the site settings section.
8) Tap on ads.
9) Ensure that toggle is turned on.
With such initiatives, pop - ups will stop functioning. If there is the recurrence of the problem despite such initiatives, there are possibilities of virus present in the mobile and the same might be corrected with your original mobile supplier with the assistance of customer care centres.