Google Adwords is a form of online marketing where you can create adverts that link through to your website or show a contact number for your business. With the usual set up of Adwords you will set a daily budget for each campaign such as £10. Within each campaign you will create ad groups which will contain keywords. These keywords can then be set either a group maximum cost per click or individual.
Some competitive keywords can cost well over £10 for each click, meaning if you have a low budget and chose to target these phrases your ads may turn off completely after only one visit to your site.
If you can only afford a small daily budget then you are better off targeting more niche keywords that may not have as much search traffic but will cost a lot less to target. If you really want to target the costly keywords then you will need to either give these words a budget of their own or increase you daily budget across the whole campaign.