When you place your buy/sell order, they will be queue up waiting for buyer/seller to buy/sell your order.
This is because there are a lot more people placing orders before you.
Just be patient, it might take 1 hour, 1 day or even longer to buy/sell your altcoins.
That makes sense, but then ....... why don't I see your (or anyone elses) buy/sell orders?
Maybe because I do not have enough to match the size of your order?
Partial fills not possible?
You will never see other people's orders, it's only your own order appears on the list.
I think your order will complete when it's your turn, regardless of the amount.
For example when you have 1000 bch sell order, you will need to wait until all the orders before yours to be completed.
And when it's your turn, your 1000 bch satoshi sell order will automatically fill the order of someone who has buy order of 100000 bch satoshi as partial order.
It can also be that your 1000 bch will sell to the next few people who have smaller buy order than your amount (e.g. 100 bch from buyer A + 200 bch from buyer B + 700 bch from buyer C).
You can see at the bottom of each altcoins the availability of each altcoins, this is how you know whether you can buy/sell your altcoins immediately or need to wait if the altcoin is not available.