Writing an offer can be very intimidating and can look very complicated. However, the Offer to Purchase (OTP) generally just sets out the guidelines of the purchase. Included on the OTP are : your name and address, the sellers name and address, both agents names, the agents brokerages, the day of possession, what is included in the sale, the offer price, the amount of the deposit, the conditions, the names of lawyers, and if there are any encroachments on the property. This can vary from sale to sale, but that is the general outline.
I would like to clarify a couple of parts, mainly the deposit, what is included in the sale and the conditions. By "deposit" I am referring to the amount of money that accompanies the offer as a token of "good faith". This is different than the down payment. The deposit demonstrates to the seller that you are serious about the transaction. On an average priced house of $300,000 or so, a deposit can typically be between $5000 and $10000. If the sale goes through, the deposit would be subtracted from the downpayment. The deposit is made out to the listing brokers trust account and is deposited the day after the offer is accepted. If, for some reason, the sale does not go through due to the conditions not being met, the deposit is returned to you with no penalty. The only time the buyer would not receive the deposit back is if all the conditions were met and the buyer reneged on the sale and failed to take possession. In that case, the seller keeps the deposit and can also sue the buyer for breach of contract.
In terms of what is included in the sale, it is generally regarded that the seller leaves everything that is "fixed" to house such as fixtures, sinks etc, and take with them everything that is not "fixed". By fixed, I refer to anything that is attached to the house by nail or screw. However, it is not uncommon for the buyers to request some items to be left such as appliances and garage door remotes. Those items can be negotiated in the offer. As well, at times, the seller may request to take some fixtures with them, such as a stained glass window or mirror.
Most offers will contain conditions of some sort. A condition is set out in the offer and is a requirement that must by the buyer be met within a set amount time in order for the sale to be completed. Common conditions are the condition of financing and the condition of an acceptable home inspection. Generally speaking, the buyer will ask for a few days to get these met. Essentially, the buyer is saying to the seller "Yes, I want to buy your house, but please allow me 3 days to ensure that I can obtain financing and also get a home inspection to make sure the house is ok."