New students can find out their level using the Cambridge English Test.
The official IELTS website describes the test structure, assessment criteria and scoring. You can also book a test here and do the (chargeable) progress check.
IELTS online tests lets you practice many IELTS test online for free with an automatic timer. They charge for feedback.
Note: When I submitted my answer they appeared to save it to their database. When I logged back in I could see a "100% icon" showing I had done the test, but no test was recorded and being done and I could not see my completed summary. So you should copy and save your answer if you want to keep it.
Duolingo English Test also lets you practice under test conditions, but it is not the IELTS test. (See FAQ)
There are many websites of sample tests with model answers. e.g.
Essay Forum allows you to submit essays and obtain free feedback. Many essays are on IELTS writing tasks
There are some example questions on the IELTS website. There are also three sample answers. Note though that these are not model answers and the answers does not match the example question.