First of all, take care of your voice, try to drink enough water, avoid alcohol and smoking if possible, and get enough sleep.
If you don't want to get the help of a specialist, voice coach, or singing instructor, there are numerous videos on youtube that can assist you, but keep in mind that almost anyone can upload a video on youtube, so take extra care when trying these at home.
I'd personally suggest "singing for dummies", I think it's a very well rounded book, with great exercises that will answer most every one of your questions! And try to sing over your favorite songs! The more you sing, the more you'll be a better singer!
Lia Hide is a singer-songwriter, producer, music educator, and multi-instrumentalist. Her debut album was released by EMI, she then decided become an independent artist, besides that she wrote music for a Greek theatre. Lia performed in major festivals worldwide alongside acts like Tricky, Molly Nilson or Kovacs. She also studied piano, opera, musical theatre and popular music vocals, and songwriting and has been teaching these subjects since 2002.