The accuplacer test is an adaptive test where the questions asked are related to your previous answers.

You will need to answer every question in this exam.   The Questions are given according to your skill and ability.

You can make changes to your answers before going to the next question, but you will not be able to skip questions and go back to it later.

The multiple choice questions are not timed, so you can take all the time you need to make the right choice. The essay test are timed.

Check with your school if you can carry calculators, protractors, textbooks, dictionaries or any other paper with you.
After completion of the test a report is created with your score in it, you will receive your report from your college.

Grammar and Sentence skills. 
Sentence skills and Grammar - there are 20 Sentence Skill questions of two types

Sentence correction.
Rewriting sentences.

Reading Comprehension
20 questions divided into two primary types.

Read a passage and answer questions based on the text.
Sentence relation, where a question is asked about the relationship between two sentences
Arithmetic and Basic Math and a written essay.

This is a Multiple Choice format exam. Multiple Choice Secrets - how to increase your score on any multiple choice exam.

Here are some tips for studying for this test

This is a computer based exam - information and help with computer based exams

Test Anxiety is one of the top reasons for poor performance on a test!   Tips on how to handle test anxiety here >>>

Test Prep Secrets - complete guide to increasing your score on any exam!

Practice Reading Comprehension Questions - (includes Main Idea and Making Inferences)
Basic Math (Very Basic - Long & Short Division, Multiplication, Decimals, Fractions, Percent etc.)
Basic Math II (Percentage, Fractions Decimals exponents, simple algebra, parentheses removal etc.)

More:

Simple Algebra
Advanced Algebra
Exponents
Fractions & Square Root