The primary way for users to find data in DataONE is through the ONEMercury web-based search interface. DataONE is developing additional search tools, which will get listed on the Investigator Toolkit page. In addition, there is an application programming interface (API) available for anyone to write a search tool against data one, which is described in the Developer Resources page and in the DataONE Architecture Documentation.
Searching Using ONEMercury
Using the ONEMercury search interface, you can do a simple full-text search, much like a typical internet search. If you have a phrase that needs to be there exactly, put it inside of quotes, like "soil carbon". Just put your full-text search in the Search For box at the top of the search form and click the search button.
The Fielded Search section allows you to search on some specific parts of the metadata, such as the title or the abstract. Date search allows you to query either based on when the data was collected or when the data was actually published (by the corresponding member node).
The Geographic Search feature allows you to define a bounding box around a geographic region of interest and restrict your search to datasets which either overlap with your region of interest or where the region of interest completely encloses the data set. You can select from US states or countries in order to quickly get a bounding box (with a bit of padding) based on these geopolitical boundaries.
Putting these together, you can type "eagle" into the search for box, draw a bounding box around the lower 48 US states, and put dates like 01/01/1990 and 12/31/2009 in the date search to get a query for data about eagles, relevant to the lower 48 states, and collected during the decades of the 1990's and 2000's. That query would look something like this:
Additional search capabilities are being developed to make it easier to search on scientific names and be more precise with geographic searches. As with all searching, it also takes good metadata to be able to get precisely the right data.
Feel free to experiment with the search interface while search tutorials are being developed.
Working with Search Results
Once you've clicked the search button, you should get back the most relevant results. You can filters (also called facets) to refine the search based on the author of the data, keywords used in the metadata, the organizations listed as contacts in the metadata, and the member node which hosts the data (shown as the "Datasource" on the results page).
In some cases, the metadata contains links to where you can download the data. For datasets which are fully integrated into DataONE, the Data Files button will show the count of files in the dataset and you can download directly from there.
If you would like to save a query, you can use the Email Query button to send an email with a link that will re-run the query. You can also save it as a bookmark in your browser, and you can create an RSS feed which will allow you to watch for newly published datasets that match your query parameters.