How do you invest with ETF's
First you would need to set up an account with an internet broker.
Remember you will be using tax-paid funds.
Using their online trading platform you can buy and sell shares within seconds.
"Ask" is what they are selling at. "Bid" is what they will buy back at. Note these prices fluctuate, so if you wait a while the deal may get better.
You have a cash account and you can purchase shares within that account. When you sell, there is generally a three day waiting period till the shares clear, it's called settled. Re-trading unsettled funds is a no-no.
For TSP the corresponding ETF's would be Cash= G-fund, AGG= F-fund, IVV= C-fund, IJR= S-fund, and EFA= I-fund. These are iShares, there are other matches but iShares are very consistant in their daily updating.
The Cash account pays interest for funds on hand, generally at the end of the month. Not quite as good as TSP, but within reason.
So using tax paid funds, one can construct a clone of the TSP funds, trade within seconds. And going to cash; withdraw the funds in case of an emergency. With TSP an inter-fund-transfer is free. Trades with ETF's have a trade cost plus the Ask/Bid difference. Using ETF's you can go with other indexes/sectors/etc., which there is a multitude. A good reference to the various ETF's can be found at the Barcharts web site: http://www.barchart.com/