[ses4j]

eBird. It is the defacto site worldwide for logging bird sightings. It is free, the app is simple and powerful, and you are contributing to science every time you use it. (It is a product of the Cornell Lab of Ornithology and they and other scientists around the world use the data heavily for many purposes). Also, it has lots of tools that help you learn the birds (and birders) in your area - localized histograms of sighting frequency, custom lists of birds you haven't reported yet, lists of nearby hotspots...

As far as identifying, get a field guide (Petersen's, Sibley's are good in the US). There are good forums with talented people helping if you submit pictures on reddit.com/r/whatsthisbird or on Facebook "What's this Bird?" group.

[mongol]

Ebird may have larger reach than any other but species sightings databases are usually mainly local / national. There are more records stored in these local databases than in Ebird. So I would answer, "it depends where you live".