Some sing & play at the same time, others do one or the other. It's all Ok, it's about enjoying the music. If you have a true desire to sing & accompany yourself playing the guitar & do both well, then I suggest you seek a competent guitar instructor who uses a well rounded method book such as the Mel Bay class method --lots of different sections re: strumming chords in many keys, arpeggio fingerpicking, "blues", playing melody by reading the notes. And of course, the strumming & arpeggio accompaniment are for SONGS, which are meant to be sung, and the book will have the melody notes, chords, and words. Or, you might attempt to use a similar such method book on your own, but if you need assistance, a good instructor is one who guides the student through the basics, allowing the student to develop his/her style & preferences, and of course encouraging the student to play with other musicians, and perform for eager listeners, such as senior citizens, especially in a group of other musicians. Seek out a "slow jam" or a beginner friendly jam in your area. Ask friends to get together with you & play & sing familiar songs--at a reasonable tempo, not lightening speed. In other words, just keep on pickin' & singin'! Good luck.