YaCy is a very powerful, highly sophisticated, feature rich, free, open source, completely configurable search engine. It can work as an adjunct for a single website, a search engine for a LAN, use it as a personal webcrawler or you can create or join a world wide peer to peer distributed search engine network. YaCy tries to be simple to install and simple to use, which in a sense, it can be, but a common complaint is that it doesn't work out of the box. Though more powerful and more effective than a simple online search engine, with YaCy it is necessary to make some decisions. How will you use it, where will you use it, for what purpose, where do you want to begin crawling and indexing the web, what type of data do you want in the database, how large do you want to allow the database to grow, etc.
If you simply install and start using YaCy, it is likely to be a huge disappointment. After all, you have not crawled the web, you have not indexed any of your own favorite websites, your personal database is completely empty, basically the search engine doesn't do much, or do it very well, because you haven't set it up.
YaCy is so powerful, so configurable, so feature rich and so sophisticated, it may be too much to handle for many. Exspect a steep learning curve. It will be necessary to watch the tutorials, read the forums, ask questions and open up the hood of this search engine to configure it to do what you need it to do.