See how an endpoint executes your query. Run a query on a QLever endpoint (the default tab uses the QLever Olympics dataset), then open the Explain tab: the plan shows each operation with its rows and time, and the algebra shows the query as the SPARQL specification translates it. Or load a sample plan without an endpoint.
Public endpoints, to run a query and fetch its plan live (then press Run):
Recorded plans, without an endpoint: